[Yoda]

Agreed


I am not talking about either of those centers per se, but about the
radius of the circle of a point from the pivot center, to PP1 - the line
in 3 demensional space. While the 'length' of that radius isn't constant
during the entire swing, its plane is (ideally, given zero plane shift).
[Bold by Yoda.]

I'm all for 'orignal thinking' and write this post in that spirit.

In a Zero Shift Stroke, the Hands and their On Plane Pressure Points (#1 and
#3) swing on the Turned Shoulder Plane. That Plane is by definition
Flatter than that of the 'Point between the Shoulders' Plane -- the Squared
Shoulder Plane you have described. [Or at least that I think you have
described.]


Also, I do not understand why this 'Spine to Pressure Point radius' concept
is relevant. Given the Primary Lever Assembly (Stroke Radius)and its #3
Accumulator and Rhythm, what does it contribute?