I’m always conscious of where I break or acclerate rocker relative to fin position; typically before or after, not mid fin. Though many times I’ll break outline with a wing or bump mid fin. When you find that “sweet spot” on a particular board you want to evaluate why; checking rocker plan,volume distribution and thickness, outline width /configuration, and fin position. Maybe just too many variables to wrap one’s head around, even before you get to the numerous varaibles inherent in various fin designs. But simply, if I have highly rockered board and the waves are mushy…I’ll get more drive and speed from a stiff, wide base, high area fin or set of fins. A flatter rockered board can be loosened up with more a vertical, shorter based, and shallow depth fin with lesser overall area; here you get more drive from the larger planning surface of the board to a point where it may be a grag at higher speeds, unless you can rocker back on a smaller planning surface where the drag might decreases due to lessened wetted surface area. Very general basic stuff here, there loads of other variables and factors with out even getting into conditons, materials and weights.