When experimenting with FOC, while using a field tip, any differences suggest the spine is being affected. If you're shooting a spine that is way too stiff, increasing tip weight won't make as much difference as having the correct spine to begin with, and then making it too weak with a heavier tip.

If you want to see the differences in various FOCs for your setup, I'd suggest tuning at 40 and 60 yards, in higher wind, while shooting broadheads. Whatever is wrong, will show up. Experimenting with FOC under these conditions will clearly show the differences.