Acoustic panels on ceiling

One more point just for future reference. Line sources or linear arrays the best of which extend from the floor to the ceiling do not send almost any energy to the floor or ceiling. If they are dipoles they don't send almost any energy to the sides either. The only reflections you have are to the front and rear walls and only the reflection off the front wall is early enough to matter. 

Jetter it is a bit difficult on ceilings but you have to find the early reflection point. To do that you sit in the listening position and have somebody else hold a mirror against the ceiling and walk slowly between you and each speaker. when you can see the speaker's reflection in the mirror that would be that speakers early reflection point. Then do it for the other speaker and place one panel for each speaker centered on those points. The trick is to find a way for that person to do that. Either a ladder that you have to keep moving or a mirror on a long handle. The mirror has to be flat against the ceiling. The other way to do it is with a laser. You shine the laser on the mirror and when it hits the speaker you have it. Have fun!,
Mike