[Yoda]

Perpendicular to the ground? Isn't that only with vertical hinging?

No, I was referring to Horizontal Hinging, the "Ideal Application" (of Linear Force) and its "perfect vector alignments" (2-C-1). Here the Left Wrist is held perpendicular, i.e., Vertical (neither Turned nor Rolled) to the horizontal plane, e.g., the ground, through Impact, thereby imparting an identical, 'Closing only' motion to the Clubface.

Alternatively, with Vertical Hinging, the Left Wrist is held perpendicular to the vertical plane, e.g., a wall, thereby imparting a Layback motion to the Clubface. This Action tends to disturb the original contact point of Clubface and Ball and results in a loss of Compression.