If you can localize sounds coming from above you, then the Atmos-enabled upward-firing speakers will be able to trick your hearing.

Sounds coming from above bounce off your shoulders and outer ear (pinna) to create a notch in the frequency response. This notch lets our ear-brain mechanism know the sound is above us.

This notch is built into Atmos-enabled speakers, which is what tricks us into hearing those sounds from above. The fact that they are pointed at the ceiling just re-enforces this illusion all the more.

The notch is also inserted into the target curve of the receiver's room correction, to keep it from undoing the notch (flattening out the response).