Despite buying a 2nd home outside of the city, I'm still stuck with a.. wait for it... small, square listening room! D'OH! Oh well, time to try to optimize around a mini-monitor midfield setup.
Playing around with room treatments so far, sounding pretty good. Tamed the early reflections on the sidewalls, adding some diffusing panels to the front wall, trying to figure out what to do with the rear wall. Going to mount some panels to the ceiling next.
The other counterintuitive experience I continue to have is better sub-bass by keeping the REL on a platform. Whenever I have an REL sub coupled to the floor, I get some kind of node activation and the room rattles with sloppy, overblown bass. Keeping the REL on a platform keeps the bass tight and snappy, but deep enough for my needs.
Nice to see you "playing" with room acoustics. My two cents about your setup: 1) with a 9" ceiling in such a small room, the ceiling is the last thing I would address, 2) since you must have limited room behind your listening position, placing the diffusers on the back wall will be much more beneficial than up front, and 3) 4 corner bass traps will improve the issues you have with your sub, or at least 2 of them in the front corners. And definitely move the sub away from the corner to just about anywhere else. You can check my house of stereo system to see how much I have been "playing" with room acoustics :)