Yep, Arthurs' the man. That is one of the best videos I have seen that describes archers paradox. I use it in the store to show customers why it is important to have a properly spined arrow.

An arrow flexing after releasing the string goes through paradox. It bends side to side. If the bend is too great, you are under spined, too little, over spined. If over spined the feathers will take a beating from hitting the shelf plate too much and/or hard. A properly spined arrow, usually achieved with a 15 yard bare shaft, will bend around the riser of the bow and stabilize when it passes. Some of the top edge of the feather will touch the shelf but, only the very edge should do so.

BKE, you say the nock is dead on square with the shelf? Meaning the arrow, while on the string is level from shelf to string? Is so, it is too low. If you shoot split finger, start the nock 3/8" above level, Gradually increase 1/8" at a time to 1/2 or even 5/8" above level. Some where in that range you will find the sweet spot. If you shoot 3 under, start at 5/8". I have rarely seen astrings nock point be perfectly level and shoot well.