I scanned through this and did not see how they appear to fly on a long shot. If my wood arrows appear to fly nice and I have one arrow with a mind of its own, I check that arrow for straightness and I change the nock. A slight nock problem can cause a consistent miss. If my wood arrows appear to fly correct and stable on a long shot and if I do not see any problems with the 'S' curve, I declare that I shot that arrow where it went. As an example, when I shoot a bow with a deeper sight window and more center shot, even though the arrow may fly correct, my first shots will show that the arrow will hit to the bow side. If I have been shooting my recurve and then shoot my longbow, the arrow will appear to have moved away from the bow. I then end up shooting a few arrows intentionally split image aiming, I almost always find that I am pointing the arrow in the direction that arrow is missing. Once the correction is grooved in, things seems to automatically repair themselves.
He pointed out that he has had an increase in draw length, if he is purely instinctive aiming, there could easily be things going on that can be moving the nock of the arrow to the right side of the sight line at full draw and the arrow is pointing to the left and off the eye line. I would suggest to make certain that the arrow is under the eye and in line with the target at full draw. If he is a split finger shooter, I would suggest to anchor with the middle finger on or near the corner of the mouth and cant the bow, if the test shots are being shot downward and only ten yards back, the bow should have a considerable cant.