Do you come from a slalom background? If so sailing modern wave/freestyle boards upwind is a radically different technique, imo. Weight forward, lots of front foot pressure, sail it off the windward rail not the fin; this is how you sail a very underfinned board (which often FS and wave boards tend to be) upwind. Sail it off the fin like a slalom board and you'll have to foot to get enough lift on the fin and you lose a heap of height.
That's my technique anyway, seems to work