ItcheSrulik: “They started during the rishonim”
Can you prove this? I quoted the Rema and Machtzis HaShekel to prove that even when stipulating “rekikim dakim” the Poskim were only opposing the tefach of Shulchan Aruch, but nowhere near the thin, hard crackers of today.
“yemenite matzos often are thicker than one finger”
I don’t know where you get this from either. The ones I have eaten (not on Pesach) were similar to a lafa (eish tanur) and not even 1 cm. The pictures in the advertisements here are similar.