Atmos speakers create a spacious, diffuse soundscape above your head. If in-ceiling speakers are not an option or your room has a low ceiling like a basement then reflected sound is the next best option. The problem with Atmos speakers in a low ceiling is someone will be too close to one of the speakers and spotlighting will occur, which is distracting.
Dawn Gordon, a Triad Speaker dealer, installer and free consultant on
AVS Forum, thinks 9' is the minimum ceiling height for direct firing Atmos speakers. Bipole speakers will sound better in ceilings lower than 9'. I have four Triad InWall Bronze/4 Surrounds in my 8' high ceiling, they are very expensive unless you find them on eBay like I did and at 84dB a high powered amp is needed. Fortunately they are always available. The early versions of this speaker are Dipole, reverse the polarity of the rear facing speaker to make them into Bipole which is the current configuration of the new speakers.
The RSL C34E MKII is also a well regarded ceiling mounted Atmos speaker.
https://rslspeakers.com/c34e-mkii-in-ceiling-speaker/I still use the Vifa Surround Bipole speakers I built in 1995 as my rear height speakers. Helicopters go up the rear wall and over my head all the time, which is just about all Dolby Atmos is used for these days.

I flipped the Vifa Surround speakers upside down creating a huge sound field at the back of my room. Cabinet design was a meditation on angles.
And 8 drivers really fill up the back half of the room during action scenes.
