my room is about the size of the OP's. i had to pull my M3s about 2.5 feet in from the back (longer) wall to optimize the sound. they were not as sensitive to sidewall distance - i have them about 5 feet from each other, and not quite symmetrical in the room due to windows/furniture etc. the thing that i found through accidental experimentation was nearfield listening. as i moved the listening position closer to the speakers the better they got - up to a point "touching distance" from the speakers, which i find optimal. this helped alleviate the backwall distance issue too - the speakers move out into the room but the listener does not need to keep moving back.
the tonal balance is full range. the soundstage can be even wider than the room and extends from just in front of the speakers to behind the back wall. nearfield provides a very front row presentation, or almost like being on the stage with the musicians. vivid. alive.
in my set up, zero toe-in works best- in other words speaker baffles parallel to back wall. there are no room treatments in my room.
so YES M3s can work great in small-ish rooms. (and correspondingly with low-ish powered amps)
i encourage those with small rooms (and perhaps large rooms too) to experiment with nearfield listening positions. and nearfield with spatial deserves a thread of its own.