Adding to this thread on 7-23 par. #3 , I would include for thought, 7-13 Par #2;
Homer Kelley wrote (6th edition)
7-13,par.#2
“ When the Shoulder moves on the same Downstroke Plane as the Hands it provides its greatest suppurt and its best guidance to the Stroke.”
As an sub-comment I note that Homer Kelley does not associate TSP. It may be mentioned, implied or assumed for some procedures but, although, it may be my oversight, I have not found it from HK.