When the ball is partially buried, you have to make a steeper swing to get the club under the ball. To do this, I keep most of my weight on my front foot and hinge my wrists quickly as I take the club back. With all that wrist hinge, I don't need to make as big an arm swing as I do from a standard lie, and the club still should enter the sand an inch or so behind the ball. It's not a dig, and it's not a skim. Feel the wedge exploding the sand.