I like to have a center above and under the screen. The problem with doing that, however, is the lack of processing for two center channels. Not many, if ANY processors have independent center channel adjustments. Delay and loudness are what I'm really after.
But to the OP, as long as you can adjust distance and loudness to match your mains, you can mount it over the screen without much issue or concern. It is more ideal to have the tweeters at ear level, but that's not always practical in any home theater setup that does not use a perforated screen with speakers behind it.
