Based on what I have read, you don't need ceiling mounted speakers per se for atmos, all you need are 7 speakers. Therefore a 5.1 system plus front heights (i.e, mounted on front wall), or simple a 7.1 system, without any heights, will activate the atmos listening mode on the receiver. Atmos, from my experience, is as much about horizontal presence and movement at it is about the vertical.
Front heights, may be enough to present a convincing sense of movement and presence in the vertical plane, with the added benefit of negating a ceiling run. The remaining 5 speakers can handle the horizontal.
I have had the klipch 280FAs for a while, but only recently hooked up the built in atmos enabled modules. My ceiling is flat and smooth, with 5.6 feet between atmos speaker and the ceiling. Apparently Dolby suggest a minimum of 6 feet of vertical clearance.
My initial experience watching the Mechanic was better than I had expected. I actually ducked down inadvertently in one of the scenes where the chopper flew overhead. It was quite convincing.
However there are drawbacks, quite a few of the scenes where the overhead effect was attempted were not convincing. And in some of the scenes where the overhead presence was felt, the sense of motion was limited. For example, in one scene where the chopper approached from the back to the front, it felt as though the chopper showed up out of nowhere, to appear immediately behind, and disappearing immediately in front of the listening position. I assume the sense of movement is limited to the point of reflection off the ceiling.
Ceiling speakers are just not healthy to a marriage that has already tolerated so much of this hobby. Therefore, if I wanted more realism on the vertical plane, I think I would add front heights, instead of another pair of atmos enabled speakers.
In sum, I think the klipsch atmos speakers perform well at an exceedingly difficult job. But at times the limitations of the technology are all too apparent.
Correction: at least two height speakers are required.
Good luck.