Set hands back to hit behind it on bunker and flop
The coach applies the hand-position idea to the short game: setting up with the hands back makes you hit behind the ball, which you want on a bunker or flop shot. For bunker shots he sets the hands a little bit back and aggressively swings through to blast the ball out; for a flop shot he puts the hands back, weight forward, and swings aggressive so he hits behind it.
Channel: SagutoGolf
Watch official source at 6:22Why this context matters
Contrast to the full-swing hands-forward key: hands back is deliberately for hitting behind the ball.