TLS is right. You can’t reasonably do in ceiling sides, rears and Atmos. It’s not made to work that way. Whoever told you that should be fired. Or at least have a stern talkin to and some kind of training.
LCR at normal locations with IC surround isn’t horrible. But it’s not as good as proper placement, and all in ceiling would be a waste.
Btw, I wasn’t sure I read the op right. Is the LCR IC too?