Regardless of what the Easton charts say I always use the full length of the arrow, too. It's all part of what's leaving the bow. But you are picking a straws worrying about .5%. Anything around 10 to 15% FOC should be good. I've shot broadheads with as little as 8% and as high as 17% with equally good results at normal hunting distances. The lower FOC will often allow the arrow to drift at longer ranges. You just have to do your own testing and see what works best for you.