[Weightshift]

I quoted from text that Lynn posted, not sure if its from the book. I understand the inclined plane and all that but in the passage there is a distinction made between "down" and "toward".
I took it to mean 'driving toward the plane line' but not 'down the plane line' hence I can't discern the difference.
CW

You are driving the grip of the club in a circular motion so at start down with e.g. drag loading, the direction the end of the grip is pointing cannot be towards the ball but only towards the plane line. Strictly speaking any applied force is tangental. When you get into the release area you the driving down the plane line to impact. That how I see it.