I bring my strong hand onto the grip with my thumb flagged high. Maybe a third of my thumb is blocking the back of the slide when I first get master grip. As soon as I start lifting the gun upward, space is created on the left side of the gun and my thumb starts sliding over there as I lift the gun. Before the muzzle clears the holster, that thumb has slid completely over to the left side of the gun and the slide is no longer blocked.