I have been trying to sight in my hk 91 and have been unable to get enough elevation out of it. I am using the sight tool but the most I can seem to raise the poi is about 3 inches and I need about 6 more to put it on at 100 yds. I am shooting Cavim ammo but nothing else shoots to point of aim either. What am I missing? The instructions are not too clear.The 200 yard sight setting is about right for 100 yds.