On flat serves, I make contact high on the stringbed. Makes sense, as I'm aiming for full extension and get the most bang for the buck at the end of the racquet-as-lever. On volleys, I also use the upper half of the racquet, as I feel it gives the most control. On groundstrokes, my racquet's sweetspot is low in the stringbed. Nevertheless, I tend to strike the ball slightly higher. Thus, I should probably raise the sweetspot using lead tape. Are there optimal places on the racquet face for contact that vary from stroke to stroke?