Something interesting to try is to record frequencies about a minute each - plain sine waves - at 1kHz, 75Hz, 153Hz, 192Hz, 200-50Hz in a sweep, and 450Hz. Play each one back through your monitors and walk around the room and see what you hear. If you stand on the sides of the room in the middle of the room, and the corners you can hear what is happening in the reflections and where the frequencies cancel each other out. I was shocked when I went to the middle of the room and there was no bass. Zero. It was like a vortex in the middle of the room. Very interesting.
SOS and other places online, like Real Traps, has diagrams of how traps should be placed in a studio.
I'm not an expert on this.. I've been prodded and poked along.
Susan