bigger fins will not enable you to hold more edge... bigger fins will help you hold track better... but edge is edge. purely by definition.
small, or no, fins you will still be able to hold down a good edge if the rail of the board is sharp (ie, the board is square edged and not rounded or thick). lean back with both heals to get edge... burying your back heal is where you will get your best power killing edge from, put the tail of the board deep with the nose pointed where you want to go... kill off more speed by pointing the nose further upwind, and stamping harder on your back heal.
when you ride in light wind with the board flat, your weight on your toes more, this is when big fins can be handy... when you are riding your board in high winds those big fins will break loose (against the water) as you begin to edge harder... they can even make some boards go "slushy" in their responsiveness on an edge. the feeling of "being stuck on tram tracks" is because of big fins
big fins are great if you want to ride the board flat and be able to track well, without being pulled off of your track... but that is not edge. purely by definition, again.
rant over
and keeping pressure on that rear foot are also very important. My two cents worth... Good luck. Oh.... don't fly the kite too high. You will get more edge control with it lower in the window.
