I placed a red dot scope on my pistol and went to zero it yesterday. I started at 10 yards to make sure it would even hit the paper. I zero it at that range and then moved to 15 yrds and the impact points were 2to3 inches above the target. I zeroed it and then moved to 25 yrds. Once again it was 2 to 3 inches high. What am I missing? I don't have any experiences with a red dot so I don't have a clue.