Good post, Raud. The only thing I would take exception to is: “It should not require adjustment of the head.” What you state is what is taught these days, but it is not what has been practiced in the past, or is practiced by everyone today. For example, one of the accomplished archers a few years ago was Jim Ploen, who taught tilting the head over the arrow. One of our best archers today is Jason Westbrock. I don't know what (or if) he teaches, but if you look at his videos, you will notice a definite dipping of his head as he is coming to anchor. The same is true with my mentor, Rick Welch, whose final movement to anchor is lowering his head to touch his nose to the feather. Not that I’m in the same class as these guys, far from it, but I tilt my head so that I can feel the bone under my eyebrow contact the string.
I think the beneficial result of the head tilt in all the cases I mention is first to establish another anchor, and second, to reduce the distance between the dominant eye and the arrow, which reduces the point-on, and the gaps, at our commonly shot trad distances of 15-25 yards.
Not that there is anything wrong with keeping the head in one position; just that there is more than one way to skin a cat.