I had my S-30 surrounds up on the ceiling(behind me about four feet).
The movie immersion was just ok,then I put them on stands(at about three feet in back of me) with tweeters at ear level and what a huge difference for movie immersion.
I wouldn't have ceiling speakers even if they were givin to me.
For 5.1 or even 7.1,ceilings speakers suck big time.
I bet even if you had a foot of space behind you the would sound a hell of a lot better than rear mounted ceiling speakers.
If I remember right (Ethan Winer chatted about this)where with Dolby Prologic they used in big theatres years ago it was used to create some ambiance.
Now it doesn't apply and that can be tested as I did the switch and its a huge difference.
I'm sure with Atmos its a different ball game altogether,but for 5-7.1,no ceiling mounting going on here and its major difference with the REAR SURROUNDS on stands,major difference for movie immersion.