I added a 3/4" rib to get my head up further. With my preferred POI I have to place my head down a little on the comb which causes my pupils to be above center. Adding the higher rib allowed me to move the comb up more yet still keep the same POI. For me adding the same 3/4" to my comb as the rib kept the same POI. Keep in mind as the head move up the pupil should also be moving down. Not saying it is a 1:1 ratio.