QB's who are listed at 6'3" are tall enough. If you assume he's 2 inches shorter than listed, you have to assume everyone else is 2 inches shorter than listed so it's irrelevant and why even bring it up? Does it matter if football 6'3" is legit 6'3 or actually only 6'1" All long as his 6'3" is the same as all other players 6'3" he will be just fine.
I've never understood the whole seeing over the line anyway. A person's eyes are probably 8 inches lower than the top of helmets so you would have to be 8 inches tallet than the oline to actually see over them.