Bud,
I think you cannot have too many reference points.
For me, the first point is bone on bone alignment, Then a repeatable head position (without this, the rest will be variable), Then multiple facial points for the string hand.
An example that I use (and have posted several times) is that 1/8th inch of deviation of the string hand (up/down, left/right, or back & forth) will produce an 8 inch error at a 20 yard target. That is a diameter of 16 inches. Depending on your definition of a "flier", how precise should you be? Starting with bone on bone, then head position, then hand position on the head, how easy is it to deviate 1/8th inch?
For what it's worth, trying to maintain an aim during the draw also causes large deviations because you are trying to conform your drawing action to an unneeded and artificial outside input. JUST my opinion, I know many do this, but I just don't see that it is beneficial.
Arne