I had some pronation issues on serve due to way too much baseball playing in which I threw sidearm (shortstop), then played lacrosse and shot with some of the same motion. This resulted in an unstable wrist on serve and made injury a lot easier. In working past this, I have been retraining myself to use a loose arm and whip through the ball. I find that part easy to grasp, but getting it consistent was tough. Anyway, I was working on hitting more of a kick serve..just hitting up on the ball and over it. What I started to notice was that this was allowing me to pronate through the ball properly and finish with the racquet butt end up pointed up. Once I got this part down, I started noticing that I was able to hit some rather big serves and was not just limited to kickers. The adjustment I made was visualizing the racquet face facing my back on the racquet drop and leading with the blade. Instead of thinking of chopping the ball in half with the blade, I thought about attacking the ball with the leading edge basically being the 3 o clock area on the racquet face. It is tough to describe, but basically how you would hit a kick serve. I was wiping up the back and through the ball instead of just brushing it with spin. My old motion consistent of my racquet coming at the ball with the edge leading, but the racquet was not laying across my back, but more straight behind me. This seemed to make it tough to control the swing up to contact and proper pronation. Not sure if this makes sense, but basically the amount of spin and pace plus consistency from this motion seems to really encourage a healthy "snap through" the ball and results in some serious heat and action. Started wondering if this type of service is how many servers hit a flatter ball that still can drop into the box with a lot of pace and accuracy.