As you quoted in your original post, any bend at Impact Fix should also be present at Impact. He doesn't start from Impact Fix, though - if he did, it'd probably look exactly like Impact!
You got me! Not really a Fix address is it? Do you have any down the line sequences? I'm looking at the one in a book called The Methods of Golf's Masters. He's definitely Arched at Start Down. Hard to tell if the Arched condition is maintained all the way down and through.
Frame 10 from the face on view shows an arched wrist at impact. That frame is basically the "separation" pic but you can tell the wrist is more foward than the hands and if you drew a line from the shoulder socket down the arm and to the clubhead, you'd have to make a "left hand turn" around the wrist. Meaning the wrist is arched.
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I'm not a TGM or PGA certified Pro, but I did stay at a Holiday Inn Express last night