I have an AR 31 and noticed the same thing. I found out that my cams were out of time. Make sure his cables line up with the serial number on the cam. The cable should cover the number if the bow is laying flat. If they are not send him to his pro shop and have them adjust the the timing. This being said AR's still do not have that great of a valley, they want to creep but if the bow is set at the correct draw length and everthing is tuned and in time he should notice a big difference.