A big flat surface between your speakers produces an early reflection free zone. This can be good or bad. The reason it could be bad is that too few early reflections can color the sound and skew the imaging worse than more but weaker early reflections. The TV isn't diffusive, so it becomes an early reflection dead zone, making it more important to deal with early reflections from the floor, ceiling, and side walls using combinations of diffusion and absorption. There will be sounds directly from the speaker bouncing off the screen at an angle and then heading toward the opposite side wall, and then bouncing back toward you. Treating those sidewall locations as well as other early reflection points may improve the imaging.
One thing I do is mount my TV higher than my seated eye position, and then angle the screen down so that it's squared up with my angle of vision toward the center of the screen. I'm not sure what this does in terms of sound quality, but at least it eliminates the parallel surface problem between the screen and the wall behind me.