30 is definitely too high. It's good to hear you have a broad range to work with though. Cost is still up in the air, but after some testing you may just find the "goldilocks" pizza stone.
I suppose we could also just up the alumina content to reach at least 10 or better.
I'm not worried abut the cost until I get something that works.
This is a very minor applicants work for us.
If I wind up with the perfect stone that too expensive, it won't be the end of the world.
We specialize in small custom runs, so this is a perfect fit for us. We have over 30 compositions on our books, but we typically only produce 7 or 8.