anchor sight

Well I just purchased the anchor sight two weeks ago and replaced my peep sight. I have shot fifty arrows two times since buying. The first group i sighted in were high 6 inches so i dialed it in and shot thirty right on. The second time i shot fifty and all were 6 inches low. I am planning to adjust my sight and keep shooting. I will practice practice practice and see if its a consistancy issue. Anyone made this switch and had simalar problems? All in all I do like the fact that after you get a little comfortable with it you focus way more (it seems) on just the pins. Thanks for the advice!