That's up to you. Back when I was in the Army, we didn't have flat top AR's. We were just starting to get into red-dot aimpoints and, we had carry handle mounts for them. Yeah, cheek weld is an issue with mounting it on the carry handel but again that's up to you. If you want to cowitness, you'll either have to mount the scope on the receiver and get a flip up rear sight or get a quad rail hand guard to mount the scope on. Either way, it'll cost you at least 100-200 dollars extra to get your AR set up in a way that allows you to co-witness.
Flip.