Seems at 40 yards your arrows should definitely be stabilized. Do the walkback for your center shot. Put a target at the top of the bail and shoot an arrow in the center or adjust your site till it hits center. Then drop a line down from up above the center of the target and this will give you a straight up and down line from the center of the target. Then step back to 30 yards but still using your 20 yard pin shoot another arrow. Then step back to 40 yards and still using your 20 yard pin to aim at the target shoot another arrow. You keep going back till you run out of target butt to shoot at. Then go look at your arrows. IF they look like this/ with the top being your 20 yard shot and the bottom being your longest shot , then you will need to adust your center shot in toward the bow for a right handed shooter . If you need to adjust it then go back to the 20 yard and set site to hit center of target again and start going back again using just your 20 yard pin. Always move the rest in small increments , a little goes a long ways. Once you are done your arrows from shortest to longest shot should be staight up and down from each other and you will have your optimum center shot .