Mo_,
I shoot most of my short bows NA style where the bow is nearly flat to the ground or at least way past 45 degrees. If ya shoot the bow in a vertical attitude then spine is gonna be real important but archer paradox (windage) becomes Asmuth (elevation) when the bow is rotated toward the ground. If it helps you at all I have never spined a short arrow.....ever. The weight makes a bigger difference because it affects speed (velocity). Also that heavy head stuff dont make any difference either, I've got 30 grain flint heads and 180 grain steel heads and heavy shafts and lite shafts and at 20 yards and under it does not seem to make a hill of difference. They both penetrate very well, and both are quiet and both fly true....for what that may be worth.
Hope that helps.
rich