JH, if you have room, about 4-5' behind you would be better than 2'. Also, they shouldn't be directly over your head, if that's what you mean. Separate them widely enough so that one is definitely to the left back and the other to the right back of the listener(s). If you can do that, either type of speaker should be adequate, but M2s should give a little more precise localization of effects in movies intended to be in the rear. With back surrounds in play the side surrounds should be directly to the sides of the listening position.
