I use an 8x8-inch stoneware pan for the same reason, keeping the peppers from falling over. I noticed that the bell peppers with 4 bumps on the bottom instead of 3 stand upright better but even those are uneven sometimes.
According to Rouxbe.com, which is an online cooking school, putting hot meat on a flat surface traps the heat between the two, effectively steaming that side of meat. This in turn causes the structure of the meat to relax and open up, letting the juices flow. Putting it up on a rack lets the air flow equally around it.
After taking that class I tried two ribeyes cooked the same way and rested them with one on a plate and one on a rack. The rack rested steak had a little over a third of the leaked juices compared to the plate rested. Since then, I've always used the rack for resting steaks or roasts.