Tom R.,-- the gap in the kettle was just for the experiment. E&E have a chapter in their DVD on Building RMH's (8" Bonnie on the cover) where they keep a couple of fire bricks near the feed for adjusting air flow. It shouldn't always be 7.5"x7.5" Thank you for the consideration!
Glenn-- I never considered the old, "big hot container of pyrolizing gases" trick. Therein, lies the rub. Flashback... end of story. To that end I recall once (and only once) covering the embers on some burning sticks (using a spare piece of refractory wool) to concentrate airflow. Wrong. I should have covered the open space-- the other side of the feed tube so the concentrated air would pull the smoke in. When I lifted the wool to peek in, WOOSH, a big ball of smoke right in the face. Lesson learned! Yah, I can see that happening with a stove door. Thank you!
S.A.-- I guess the search terms I put up didn't jive. I've not read thoroughly through all the threads. But FWIW, I've been studying two years before making the leap to build my current heater. This is just a quick question with a short answer and I got it in just over two hours. Thank you anyways!