I would try out a little further before changing anything, 15, 18 then at least 20. If you're speed is slow enough you can see how the bareshaft flies. In fact I say this now that I would wait, try further, try every couple days like rifleman says but my lack of patience would get the best of me and I would end up being too stiff. I try to get my arrows a tad on the weak side. When tuning I seem to be more aware of my draw anchor. If I'm just shooting or hunting, I can get sloppy and I hope the weaker arrow compensates for the slop.