An oldie but a goodie. A bit of an update, I said you sit into left heel, you actually push down into ball of left foot and that force coming back up opens the left side of hips. Bob Torrance always said back in the day the worst move you could make was straightening you left leg independently to open your hips. You must use the ground under the ball of left foot to force the hip back. More on this on #paddysgolftips on YouTube