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Perhaps the misunderstanding is that the thumb shifts from one lower (edge side), corner to the other lower corner as the razor flips.

As you flip, the thumb switches corners from the upper corner...

Good question, No, the opposite.

I always start going up, (away from the body), So the edge is facing the bottom or handle of the strop, the spine facing the top of the strop.

The middle of the...

Hold the corners of the tang, the middle of the thumb pad, upper left corner and the opposite corner, the pad of the index finger or second joint pad, as Sham and AF Davis, do in their videos.
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