I agree with you BC... it is usually a left to right issue... but here is why I think that...

I had some 400 FMJs that I was shooting off my HCA Iron Mace a couple years ago.... and they constantly wanted to go low and left. When I tried some 340 Axis arrows.... they tuned up nice. Of course a 400 at 70#s off an Iron Mace at 29"... I should of started with a .340 spine. My error.

As you know... a weak spined arrow is going to flex a heck of a lot... and that energy being used to correct flight and have the arrow flex is energy that is NOT going into propelling an arrow... so at least from a common sense standpoint to me... that change or net loss in energy potential for flight is being realized enough at 30 yards to make the arrow drop lower.

I have seen improperly spined arrows do lots of weird things off compound bows with release aids.... I've seen them kick and shoot in all directions. There are just so many variables that if we can eliminate a couple at a time it will get us much closer to the real cause of the problem.