I've been reading through this thread and love some of the results you're getting! I had planned on doing something similar to the mat you've developed, though more for testing colorant blends vs glaze ingredients.
The idea of having some sort of vertical test in a grid is really intriguing. If you had the spacing worked out correctly, using something like 12 or 24 well plates to mix glazes and dip the tiles might work. Amazon and eBay sell lots of what's meant to be disposable lab equipment that can end up being pretty cheap if you reuse. It's often used for doing medium thruput work where you're looking at a lot of variables, so perfect for this sort of application.
Also in agreement w glazenerd on some sort of g/in^2 or specific gravity surrogate.
I finally have my studio finished and kiln hooked up and excited to get started glaze testing again, though will likely be a while as we're due with our second child in a few weeks. I find the glaze testing one of the most rewarding aspects of ceramics--so many variables in terms of clay and firing cycles alone! It definitely appeals to the former scientist in me!