Reflections and edge difractions are what kill the imaging. Speakers should be 3 feet minimum from any side wall even if that means they are closer together than you would really like.
Not seeing the sound
The other day, I was playing around with speaker positioning, and hit upon a spot where I could no longer "see" the sound coming out of the speakers directly. Now, the sound seems to be in different places relative to where the speakers stand, sort of in an etherial way. I like it. This may be a dumb question, but does this mean I've finally gotten a "soundstage?"