I can hit a pretty good slice when the ball is below shoulder height. But when the ball is above shoulder, I have trouble generating pace and the ball becomes a floater and lands short. What is the proper way to slice a high ball that has a good amonnt of topspin? The recent thread on Federer's slice where it describes you hit down and across, I can do that on low balls. I can't visualize how you slice down and across on a shoulder height ball. Tips?