Exactly Jerry,spine is probably the single biggest obstacle with getting the 2 to group together.With so many trying to get as heavy as possible and ending up with overspined arrows it does make it very hard to get the 2 together.In those cases they are much better off just grouping the broadheads.Overspine as well as underspine arrows want to kick when center shot is right.The easiest way to fix it is to move the rest and that causes the 2 to impact different.If spine is not correct then the arrows need to be coming off the rest as straight as possible and imo this causes way too many problems.Not coming off the rest straight but the fact you have to move center shot to achieve it.