It sounds like a couple of things could be happening.
1) If you are not using a peep for the sight then it is possible that your anchor point changes just enough each time to be a problem.
2) I'm not sure if you've had any experience with adjusting sights but if you haven't you move the pins in the direction of the arrow. For example; if you are shooting low then move the pin down. If you have adjusted sights before then this might not be the problem.
3) It's also possible that the speed of the bow won't allow you to adjust the pins far enough down to be usable. Have you moved the whole housing down on the dovetail rail? We put a 3 pin sight on my son's Mathews Genesis bow and we couldn't adjust the housing far enough down to work. The arrows were hitting the housing.
Let us know if you were able to solve the problem.