To have the same POI, both dot and front iron sight must cowitness, but you see this only when you are looking through the iron sights. If you are not alingning your eye to the iron sights but the gun is still aimed precisely you'll just see the dot on the target and the irons somewhere else.
IME most people find it more comfortable to lift their eye line a little bit and get the iron picture in a sort of lower 1/3.