RE: p.o.i jumping 6" to 1 foot at 15 yds
Most Likely
1) Cam synch. You are creeping or overdrawing on occasion and getting that flyer. It only has to be off a tiny bit. That is why many folks "creep tune" thier dual cam bows..it prevents this phenomenon.
or
2) You've got a bad arrow or two. Number them and keep track