I have a DE 338 edge with the NF 5.5-22x56. I am shooting 3/8" groups but the center of the groups are 1/2" low at 100yards. Do i need to change this? the other day i was 1/2" high and i had to reset the zero stop and move it down 2 clicks. now it is 1/2" low and i really dont want to mess with it if i dont have to. the question is: if i am 1/2" low at 100 yards, how will that affect my exbal reading for longer ranges?