if you want real atmos then you need physical overhead speakers, or at the very least speakers pointing upwards to bounce the audio up and back down.
no soundbar is going to give you "real" atmos though.
real atmos takes many speakers, so unless you have a cinema you aren't really going to get that.
you get a simulated experience but you need to keep your expectations in relation to your cost outlay and the amount of physical speakers you have.
the rears just give you rear audio, they are not doing anything "vertical".
Though the rears do contribute to the bubble effect you get surrounding you with sound. And by increasing volume on the rears, depending upon source they massively improve the sound quality.
When I compare to my other older Sony 5.1 seperates system, I do notice the difference on the zf9. With you being immersed on sound compared to the 5.1 separates.