I found this information here but I think it would be with 2 fins?
Because our iSonic are fitted with the Tuttle fin box system, you don't have to worry about the position of your fin - it's fixed. However, do consider carefully what size fin you will fit. It's importance is often underestimated, and by a lot. See it this way: in different wind conditions, we tend to change sail size. Well in different wind conditions, you should also be changing fin size. Yes, it's that critical, and the wider the board, the more critical.
If we take our iSonic 122 for example, we supply you the board with two fins straight from the box - just to make sure that you get to enjoy the board's vast wind range. As a basic guideline, we tend to use the larger fin when matching the board to sails above 8.5m2, and the smaller fin when matching the board to sails below 7.5m2.