Well, those photos changes everything. I thought the plates were put down first, then the field carpet on top of the plates. I didn't know there was
another carpet square put on top. Makes sense, I guess, so they can reuse the field carpet from year to year. Now I understand how GDC has it "up to 1/2 inch" thick on a 1/4" plate.
Of course, this makes me a little more nervous about
this point I made about the overhead being pulled sideways by a wayward robot. I'm sure between weight and direction of pull the overhead would win, but having it only held down by carpet squares and gaffers tape I wouldn't be so sure.