I have a similar layout where my center and L & R speakers are on top of the entertainment center, nearly the same height as my rear surrounds. I do notice a difference in sound for the better when I stand (front speakers ear level) vs. sitting down.
The left to right or visa versa sound presentation doesn't really seperate because they are within 6' to each other and I'm sitting nearly 13 ft. away.
Go for some speakers that have good off axis response.
If I had a different location for mine I'd use it, my biggest dislike is not necessarily the off axis performance but the side to side surround processing not being very noticeable, it's like I have one giant center for the three front channels