I think it's extremely difficult to do a meaningfull test like this. Even the difference you have in spine could explain your apparent contraditory results with accepted physics. If the spine is different then the "tune" is different and therefore at close range the angle the arrow strikes the target is different. It would be interesting to do the down range test as you suggested. That should tend to eliminate tuning differences but then again it's still very difficult to control all the variables in a test like this. I'd rather just trust the physics. Heavier arrows mean a higher percentage of transfer of stored energy to kinetic energy. Thatis not only true in theory but also easily confirmed in tests andhas beenrepeatedly. Pick up a copy of Bowhunter or any mag that does testing and you will find that efficiency and therefore ke and momentum always increase with arrow weight. All things being equal, more energy/momentummeans more penetration than less and that's what you get when you go to a heavier arrow.