[O.B.Left]

D, I'd say you're bang on there with that quote.

I believe the "flat as possible" shoulder turn on the backstroke is ones best effort to get the right shoulder onto the shaft plane........which cant be done most likely if the club is flatly soled anyways.

Why do this? To minimize the plane shift necessary to get the Hands and Right Shoulder onto the same Inclined Plane at Top. A TSP. The TSP is not a singular plane angle, there's a range, the flatter the less the associated Plane Shift gong back and then down........which isnt necessarily a particularly flat swing in common parlance.

Understanding, employing the TSP forgoes the necessity for "vertical drop" or any other compensation that some teachers promote as "the" method. It just aint so, its "a" method only and one Homer described himself for those who choose a plane angle higher than a TSP. But I digress. Homer's Turned Shoulder Plane is pure genius. Its worth the study as its the cure for many of golfs ills which appear in transition, "at the crossroads of the swing " as Homer referred to it.