I am looking at a used Colt AR15 223 that has the handle on the top instead of the flat barrel for mounting the scope. If you put a scope on the handle it will be several inches above the barrel. How will this affect the sighting in of the gun. If I sight it in dead on at 100 yards, what will it be at 200 yards. Will there be a bigger variance than with a conventional rifle? Thanks, Comanche.