mrcasey

It seemed like a given that they can and many of us do this but I reached out to the Ceramic Shop to ask them specifically. They make, sell and wholesale posts to other ceramic suppliers in the US and elsewhere. (they make triangular and square ones)
Their reply: 
"Thanks for reaching out!  

To my knowledge, yes, they can be used on their sides. Kiln posts are made to be the most stable on their top ad bottom though and they will take up extra room in the kiln on their side. If you need a smaller kiln post for some works you can check these out:  https://www.theceramicshop.com/product/148/kiln-post-1/ 

All of our kiln posts are rated to cone 10. 

Best, 
Syd"

No worries at all.  If ever in doubt it's always a good idea to double check things and not just take some individual's word on something.  So no harm in calling your kiln manufacturer.  But there are only a few kinds of materials used in kiln furniture and you can tip any of it on it's side without harm.  Firing ceramics, despite our fancy electronic controllers and such, really is an ancient art form and hasn't changed that much even with more modern materials and techniques.  So kiln furniture is pretty basic.  Also, your kiln manufacturer almost certainly didn't make any kiln furniture you got with your kiln any more than they make the fire brick they build them with.  That stuff usually comes from just a few manufacturers who in turn supply all the kiln production companies.   Kind of like china paints - they all come from China but there are only two companies in the USA who import and redistribute it no matter who you actually buy it from.

No offense intended - I agree with you.  Some folks in our community studio thought it was an issue (which I thought sounded off base), and I just wanted to make sure.   

I have used  kiln posts on their sides frequently.  Sometimes the side measurement gives you just the right height that you need.  No Problem.  Lin

You do know this all predates 'manufacturers', right?  People have been using kilns and kiln furniture for thousands of years and reusing the same basic materials to do so.  But if in doubt just call your kiln manufacturer.  You don't have to take our word for it.

Yep!  Position them ANY way you like.  I often use them on their sides to stilt pieces up off the bottom of my kiln if my equine sculptures are on bases.  Without airflow, the larger bases in direct contact with the kiln floor can retain a LOT of heat where as the slim legs above may cool too fast and cause the pieces to break.  You may also stack your kiln posts to 'build' walls.  I also have an assortment of other kiln furniture that was given to me but here's a really sweet tip.
You can buy materials to MAKE YOU OWN custom kiln furniture and stilts.   I've done this in some cases where I really need special shapes and then added various thickness of Kanthal wire to run up into pour holes or whatever for especially delicate pieces that would other wise fall over during firing.  Or you can skip the specialty materials if you need one use supports custom fitted to ware by making 'setters' instead that can shrink with your pieces, such as used with porcelain bodies.
Anyway, I digress.  No harm at all in utilizing your kiln furniture turned this way and that, or stacked.  I've even used bits of broken shelves that were given to me for nothing and busted them up to the shapes and sizes I needed.  You can even get or make  'kiln beads' that you can box to form customized supports and nestle ware down into.

I remember classes from Penn State in the Summer with David Dontigny where he stressed thinness of the raku, but insisted on thicker rim areas as the tongs would sometimes abuse the rims. We threw an entire Summer with that heavily grogged clay and I had permanent sores on my first, third and thumb knuckles from the sanding they got. Never kept a single piece of that summer. Throwing  loosely was counter intuitively to me at the time, and I hated the pieces. Still see some around town, but don't admit to them.
 
best,
Pres

It will actually survive the thermal shock better if it is thinner, because it will cool more evenly. The thicker the walls, the greater the difference between the temperature of the inside and outside surfaces. That difference is what causes cracking because they are contracting at different rates.
IMO, functional work should never be more than 3/16" thick unless it's very large.

The big caveat to anything raku is that for every rule, there’s an exception that proves it. But in general:
Thickness isn’t a guarantee that something will live. A poorly constructed but chunky piece can still break.  You want to think clay body, and construction methods. 
Clay body can have a big influence on your results. If you’re using a clay that is sold as a sculpture or raku clay body, it’ll withstand a lot more thermal shock than one that isn’t. I’ve seen people create small, very thin-walled pinchpot style animal figures out of a groggy raku clay with minimal problems. I’ve also seen thick walled stoneware pieces shatter within the first few minutes of the firing. I wouldn’t suggest using a typical talc based casting body: they’re relatively friable after the bisque compared to their green strength.
You want to think about construction methods that are as structurally sound as the design will allow, and have as even cross section as possible. Curves>90* angles. You want to allow even heating/cooling over the whole piece, and avoid one side of the piece heating or cooling faster than the other. If cracks appear in a drying piece, I would not recommend repairs: start again. It will forever be a weak point, and throwing pieces into a reduction barrel can enlarge it. 
Some of the ideal thickness decision is going to depend on the scale of the piece too. 3/16” for an object that fits in your palm could be just fine if you’re working with a groggy open body. If you’re using a porcelain (which is doable) you’ll possibly want to go with a thicker cross section. Additional thickness is only useful if it adds reinforcement, not just for its own sake.

Try a test first just to make sure. It can vary by clay body. I’ve had a few pieces warp  ever so slightly in an 04 bisque, and I use a cone 6 red stoneware. I wouldn’t say it’s the norm, but it’s not impossible.

No problem at all.

I do it all the time with my porcelain mugs

Can green ware pieces like mugs be loaded on their sides in a bisque firing?  Will they have a greater tendency to warp?

I use a slab roller.  Clay is rolled out at roughly the softness at which one would throw on the wheel.  Slabs are about 1/4" thick.  The clay is then placed on sheets of dry wall for about an hour and left to firm up a bit to about leather hard.  These slabs get flipped a couple of times so that they dry evenly on top and bottom.
The walls are anywhere from 6" to 14" long. The wall corners are beveled and cut in a trapezoid shape so that the walls angle out slightly from vertical at about 10 degrees.  Corners are scored, slipped, and assembled.  I use a t square to try to get all corners at 90 degrees with walls straight.  There is usually a little bit of a gap (1/16") where the corners meet, and I fill them with a bit of coil. 
I score and slip the bottom of the rectangle, score the slab for the pot floor.  I use the t square again 
before pushing the walls onto the floor.  Sometimes, the pot will have a rim; sometimes not.  The rims are made in one piece and look like picture frames before being attached.  They are scored, slipped, etc.  A coil of clay is then placed around the outside join.  The clay for 
the coil is necessarily softer than the leather hard walls.  I use an apple corer to make drainage holes.  The pot is flipped
over and feet are attached. 
The pot is put under plastic and left upside down on drywall for a day to help keep the rim flat and level.  The pot is flipped back on its feet so that the feet remain relatively level.  After a couple of days, I'll take the plastic off.  Sometimes, I will start seeing a bit of rim bowing as the pot dries.  Often, one side will remain relatively straight but the other side will suck in a bit.  Once the pots is bone dry, I will spray water on a mirror and move the pot back and forth on the mirror to even up the feet.  
I don't have any particular place I set these pots in the kiln.  I use flat kiln shelves.  We fire electric
to cone 6.
I have noticed that the thinner the walls and longer the pot, the more warping I see.  14" long rectangles with 1/4" walls have quite  a bit of "life" to them.  I've noticed that a lot of the expensive Chinese and Japanese antique bonsai pots have some warping.  Maybe unless I want to use modern mold methods, I just have to live with it?          
 

Can you post a picture, top and bottom? The feet are probably the biggest culprit, but any time you have long flat sides like that they're going to warp. On solution is to put a slight curve in the sides, which makes them less likely to bow inward.
Any clay body that vitrifies is going to want to warp in the firing. The lower the absorption, the closer the clay is getting to its melting point and the softer it gets at the peak of the firing. Have you tried firing them on a waster slab? I wold also try going thicker as they get larger.

I wouldn’t over think it. Refires are hard on pots as virtually all fluxed reactions have already occurred in the first firing, except for the new applied glaze of course. My expectations for refires are low and if I can downfire then my chances of survival are better in my experience.