I think that part of the reason for the POI shift, is that shifting aim to one side or the other, for another bull, we do not hold the rifle the same as before. Just a slight change in hold, 1/4" high or low with on shoulder, or a diff spot on the comb, will change POI. You can still get a good group, if you keep the same hold for that bull, but when you go to another bull ,if hold shifts, POI will also shift. If that makes since. I can also shoot at single bull targets better and that is the only reason I can come up for it.
Mike