Itís good to hear you are experimenting on what might cause the pimples or blisters.
I think this has been a good topic of discussion for a long while. Even people like Tom Lehmann and other members of this forum have tried to study what can cause these pimples or blisters. People that have so much experience in making pizza dough don't have all the answers, although they havenít really studied extensively how this can happen.
In my case, I have watched the different doughs, time left fermenting, cold fermenting, time on the bench, temperature of cold ferment, warm-up bench time, bake temperatures, over fermented dough, frozen dough, flour used on the bench, and other ideas. I havenít been able to replicate any blisters consistently. IMO, I think you would need so many constants to be able to figure this out, like a controlled environment, dough testing equipment, and a desire to keep all testing on one formula until all experiments are exhausted.
What I am trying to understand, so far is how dough contains many air cells created during fermentation or proofing, and then these air cells are separated by cell walls. When the dough hits the oven or stone, the cells expand creating oven spring. Then the starch in the cell wall absorbs moisture and makes the gluten lose moisture. Maybe then lessening of moisture creates small holes forming in the cell walls. I have peeled back many crusts while eating a slice of pizza and can see where the steam has vented if the dough has been properly made and proofed. Higher moisture doughs seem to have more holes. I donít know if when the steam canít form in the cells walls the right way, if then more problems occur or if this or other conditions might form the pimples. Maybe I am not right on this, but am trying to understand. Some people can get pimples or blisters on a more consistent basis.
I have watched how one dough can poof up like a balloon if just left to bake with no topping. Watching this from a low hydration dough to a higher hydration dough, with yeast, without yeast, and different oven temperatures and they all seem to poof in the center, without toppings. I donít understand why, but they do. Those doughs donít get much oven spring on the rim. It seems to just poof up in the middle.
I will keep watching, but donít think there will be any consistent progress from myself.
Best of luck to you in trying to figure this out,