A 7 foot ceiling height is a major problem with most in-ceiling speakers. You will have to install the front and rear Atmos very near your seating to have success. If you have very wide or deep seating in the room, you may not be able to get good coverage due to the narrow sound dispersion of a speaker so low. If you go with a slightly-angled speaker, like the RSL mentioned above, the maximum distance you would be able to place the speaker, would be the same as the distance from your seated ear to the ceiling. If you are just catering to one or two seats that are centered and close together, you might have some success with that scenario.
However, if you have a wide couch, or disparate seating in the room, then your odds of success are very small with any in-ceiling design. In that case, you would be better off with a small on-ceiling speaker, such as the Cambridge Audio Minx Min 12. Given that you could position that speaker horizontally, you would gain a lot more coverage area, that coverage only being improved with additional distance. Plus, the Minx are known to have good horizontal dispersion characteristics.
Lastly, consider on-wall speakers, front and back, mounted at the ceiling juncture. This would allow you to use a bit larger form factor and eliminate the risk of hitting one's head on ceiling mounted speakers, if you have any very tall friends/relatives. Maybe a speaker like the Polk OWM3 would be appropriate for this sort of approach, or any smaller bookshelf-sized speaker.
This has recently been discussed here, if you want further development of in-ceiling issues: