Keep in mind that placing two speakers playing the same signal that close together could cause serious lobbing at certain frequencies. I noticed it when I tried it with a couple M22s. So you may have to play with how far apart you place them if you hear a noticeable change in SPL move from one side of the listening area to the other.
When possible a better configuration for two center speakers is one under and one over the screen. It keeps the horizontal dispersion from being an issue and perfectly centers the center channel image in the middle of the screen w/o having to use an AT screen.
Thanks for the tip. I'll try top/bottom as well.
