as I posted before, I would try a lower boom height first. I use new tushy t4's and lightnings and for some reason I can not put my finger on, I seem to need to have the boom lower than previous models,
(or other sails I have owned for that matter) for exactly the same reason. lowering the boom for me has stopped the nose off the board riding to high, oint higher up wind, feel more in control of the wind and the sails feel easier to handle.
ps.. and this works for me no matter if I am using large or small fins in the board.