Fillae,
Good points, also BH's will ACCENTUATE form flaws, and unless you have PERFECT form, BH's are NOT going to group as well as FP's unfortunately. But with minor rest adjustments, you should be able to get everything CLOSE. As Fillae said, move the rest in SMALL, TINY increments and re-shoot. Move the rest the direction you want the BH's to go. If you still have issues, it may be SPINE that is creating a problem. Over and Under-spined arrows do not fly nearly as well as an arow that is spined specifically to your DL, DW, and tip weight.