Gday Daryl.I`ve made a few boards and believe fin placement really comes down to trial and error.A fin placement on a short narrow kiteboard could vary a lot from a larger wider kiteboard.Board tail design and rail shape can also be a factor(and concave).what i have found personally is that the fins seem to work best for my boards (around 130cm-140cm, sharpish but not super sharp rails)as close to the rail as possible,and the rear of the fin ending about 4-5centremetres from the end of the board,this is the case for edging up wind or gaining as much grip as possible,however when talking about wave riding you could argue.This doesn`t mean go and try and drill new holes close to the rail and the tail of the board.if your board is a production board it will probably work fine in any of the positions,and the options would come into play when you become more experienced and can feel the performance of the board.start with the fins as close to the rails as the existing holes will allow and go from there.you will find when your ability increase and you play around with your fin placements eventually you will find the best fin positions for your particular riding style.

Have fun.
Karl