Or, like Rick Welch preaches, the rest might be thicker and it has moved your groups left, just as a thinner rest would move them the other way. He uses this method to make arrows hit where you look, so maybe you will have to change arrows with that rest to achieve that. Like Hermon said, moving center shot out requires a weaker arrow, usually, so you might have in effect stiffened the arrows too much and now they aren't flexing around the rest enough and producing excess wear on it. Try a really heavy point and see if they hit center again; that will tell you if you need weaker arrows pretty quickly, or whether you have some other contact issue going on.