Similar thread going on the zone:
www.standupzone.com/forum/index.php/topic,37246 My understanding is slingshot came out with the switch fuse to accommodate multiple disciplines and the foot placement requirements.
My board didn't have the track box location for A position to work. I found that b position (mast closer to front wing) gave more performance or looseness, and c (mast further from front wing) dampened it a bit making it easier when learning as the foil is not as reactive, but need the track box travel (plate further back on board) to sup foil in c position.