Actually there is a flat top to the front sight, I know that is hard to believe for weak eyed geezers like me.
The FO dot is supposed to grab your attention and get you on the front sight quickly and can be used for sighting at maybe 10 yards and under, especially for fast open shots.
For longer, tight and precise shots you should be aligning the top of the front sight with the top of the rear. Hard to do if you can't see it but that is the theory.
I have lost my FO in the middle of a stage and successfully finished the stage just using the front sight as intended.