Some people seem to get good results with equipment in the center if it's very low down, e.g., a power amp. But if it's higher up, it will interfere with the image even more than it will with boxes. Forex, I have a room with a fireplace mantle that juts out around a foot and I can't put the speakers against that wall, whereas they image beautifully against the mostly plain wall across the room.
In my experience, planars like a relatively smooth surface behind them. Ideally with diffusion at the first reflection points (the place where you can see the tweeters in the mirror).
Anyway, I think the thing to do is to experiment and see whether it's high enough to make a difference in your case.