Still cant rule out arrow problems. Your spline, or FOC (cant remember the magic number, been too long since I shot compounds)could be outta whack just a lil. The FOC is the center point of your arrow including the head, I think perfect was around 12 or 13" from the tip back, not sure though. At 20 yards you're not noticing it as much because the arrow hasnt had time to deflect. At 30, your arrow may have had just enough time to tweak a lil, and then at 40 it flattens back out. I'm not really sure, just adding another suggestion. But you may try to shoot at half yardages to see whats happening, 25,35,45 or 15,25,35.