It sounds to me like your center shot is not correct. You can cure this by walkback tuning. Draw a perfectly verticle line on the target and shoot one arrow at the target at 10 yds. move back 10 yad repeat, move back 10 yds. You already stated the arrow drifts. move the rest (in small incriments) the way you want the arrow to move and repeat. You will most likley have to move you sights in accordance.