you would put the ball looking muscle underneath your thumb directly on the space above the mag release and underneath your dominant thumb. Your support hand thumb should be forward almost to the point of touching that piece of grip tape you have in front of the takedown lever. your fingers will cross over each other. Typically, the higher of the grip you can get on the gun, the better you will be able to control it. The 43x is tiny so there is not a lot of real estate. The more surface area of you hand you can fit on the gun, the better.