Mindy says to "screw" the two fingers of the trail hand onto the grip. I believe what he means is that the grip is held mainly by the outboard joints of these fingers. Since the club is not tightly gripped by the rest of the hand I think I momentarily allow these fingers to open a bit during the initial backswing, allowing the lead hand to keep the clubhead "on line" until the trail hand grip is closed a little further along the backswing.
My own experience with the analysis of Mindy's grip is that, with the shoulder rotation of the trailing arm, it is quite natural. I have stopped trying to analyze it, since it is working for me. Looking at Fig. 13, accepting it, and figuring out how to get my arm in that position, has been a personal Eureka. Maybe it will be of help to some others.