Generally, you want the speakers, L/C/R, in a flat line. That way sound moving across the screen does not move up as moves left to right. All that said, I moved mine to over the TV and improved the clarity of dialogue. I have not noticed any loss in image quality on moving sounds, but over my screen is only about 15 inches higher than the tops of my towers, so minimal sonic impact.
Also, if you get an image to the left in 2 ch, then you could spend some time getting that worked out. Toe the speakers in, get the levels right, etc. If that does not work, you might try to treat the first order reflections. My image was off as well, but after some work I have it dead center now and music is much improved.
