I have a story about posts not lined up back in collage.
Another person loaded the bisque (36 cubic foot alpine kiln) He choose to not align the posts much near the bottom and changed the pattern 1/2 way up. He lit the kiln and left. I was throwing late that night when we heard a huge strange noise from th kiln room-as we approached the room was a mix of fine dust and the feeling something was off. We turned off the kiln and let it cool after opening the door the whole load had collapsed with very little greenware left whole.Seems the top shelve was now near the bottom shelve and all the pots where back to smaller clay pieces once again.
Years later this same guy blew up his home built catanary arch kiln-the two end walls blew out and the arch went up then down into a pile.
Years I bought all his materials as he gave up working with clay.
Now you can fudge some for sure on line ups but do it near the top of the load.
As to shelve on bottom-mine is a full with 1/2 broken shelve pieces on floor under it-the floor is always cooler and a shelve up helps with more heat.I only bisque in this kiln occasionally . I do not have a vent or heated floor
With my 35 foot car kiln to cone 10 or cone 08 the posts all line up always. I take care of my shelves and get long life from them this way. Theres not much reason ever not to have posts line up. Maybe large sculpture and if thats the case fire it on top.
One last note we all learn from our mistakes you will not know your limits until you have exceded them.