I use white worth's semolina as it's really fine and I like the added flavour from it.
what is the flour / semolina proportion you use ?
semolina is wheat so still has gluten, whereas polenta, particiant ref'd, is corn too, I guess, in a base, with polenta, it would it more cakey.
I just use polenta to help with dough handling at the end, preferably the fine stuff, bought some coarse because it was cheaper, but since it does not cook thoroughly it introduces a grittiness vs fine, seems to burn easily too, and set off smoke alarm. (polenta does not seem to sell with a 00/000 guage like flour)
I am not convinced by the stone above strategy, we don't have not got the temp in an oven for black body radiation/glowing;
the stone beneath works by conduction/contact, a big heat mass, but above, need to make sure the air flow from a fan oven is not obstructed