That's cane for ya, I find no rime or reason to some shafts. Some just don't shoot good. But, as Gut said I do think % FOC has a lot to do with cane arrows. The different tapers in the shaft can cause different FOC balance locations. Find the balancing point on the arrows that shoot good, and see how close they are to each other and to the ones that don't shoot.
Let me know what you got. I'm kinda doing a study of the FOC point that way.
DBar