Always get confused. Need clarification. I just bought an M&P15OR. I want to put some iron sights on them. I know the picatinny on the gas block, and the one on the main part of the weapon are at the "SAME" height. So, if I buying iron sights for the front, am I wanting a "Low Profile" or a "Standard Height"? Both mention mounting to a "Gas Block". I've heard stories of people putting irons on their 15OR, and shooting uncorrectably too low, because the front sight is too tall. Thanks for the info.