Many people use angled in-ceiling speakers, both for surrounds and for Atmos channels.
Some ones to consider:
RSL C34E;
Monoprice Alpha 8" in-ceiling with 15* angled baffle;
HTD HDX-R65AIM;
Paradigm CI Home H65-A.
Some ones to consider:
RSL C34E;
Monoprice Alpha 8" in-ceiling with 15* angled baffle;
HTD HDX-R65AIM;
Paradigm CI Home H65-A.