That makes sense, to think of room as integral part of the system. It absolutely is.
The last time I tried moving into the 11x12x9 room, I put a pair of usher Be-20s in there and tons of acoustic treatment to control the bass overload.
http://www.audionervosa.com/index.php?topic=1150.0 That failed not because the room was too small, but because the speakers were incompatible with the room. There's a piano in there now, but I could still try it real quick with lesser speakers. Actually I think I did try that once with little Infinitys 2ways, the success of which prompted me to move in the Ushers.
I do remember breathing a sigh of relief when I moved back into the big room, it just sounded better even disregarding the bass. But maybe that was only because I was accustomed to it. I had much less acoustic treatment in the big room then. I still like the sound of the big room. The little room will require a lot more midrange absorption than the big room to stop those early reflections. I don't have that problem in the big room.