Changing the fin position can really change how the board feels and turns. It is however very easy to tune the fin position or positions keeping to this simple rule. If you move the fin or fins forward it will loosen the board up. What this does is, make it easier to turn or break the fin/s loose. However loosening the board like this can also mean the board with be more prone to spin out as the fin/s become further under you back foot it means less force it needed to break the fin/s loose. Moving the fin/s back gives better up-wind performance, more control and speed. The board however can become harder to turn.
Fin back : These however are basic rules and the only way to tell what’s best for you, is to try. You can also use these rules to get the most out of your board in different conditions. For example I move my fin fairly far forward for snap and slide in onshore conditions.
Fin forward : I move the slightly further back in offshore conditions where you use more speed and the control is nice in longer drawn out turns.