I use a perforated pizza pan as well, but when I did the biscuit test, the ones on the outside were obviously darker. So, I switched to three remote thermometers (didn't want to ruin more biscuits) and started drilling the holes in the pizza pan bigger until I got a consistent temp throughout. I've been very pleased w/ the performance (no real hot spots) since then.
UDS / UDS / Mini WSM
Hackers -n- Hogs Competition BBQ Team
Grip it. Rip it. Let the big hog eat!