Ken Beck of Black Widow Bows, who has spent a lot of time studying arrow flight, told me that the feathers flatten out against the arrow shaft when the arrow is released, and don't open up again until the arrow is clear of the bow. This is why we can shoot arrows successfully off the shelf, but need a rest if we shoot vanes.
What causes a problem is if there is any contact between the quill (plus whatever thickness the feather is when it is flattened out) and the shelf or the riser. He recommends setting the nock so that the bottom two feathers form an inverted V shape, where the inside one can slip between the shelf and the riser. So far this has worked for me, and I haven't had to raise my nock point any higher than 1/2 - 5/8.
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