I am looking at building a 16" upper with rifle length gas tube. I am looking at a free float tube (probably only rails on top) I will probably add a 1x4 scope of some type. The question is, will the standard F-marked front sight post be in the way of the optic? What if it was an EOTech? Or Burris Fast Fire? This is my first attempt at putting together all the "features" I want. Anyone have any experiences to share to potentially save me some money?