I sail a HS111 with 6.7 RS racing in say 15-25 knots quite regularly (although lately, now that my new F93 has arrived, not a puff!) with a 34cm drake slalom fin. A wee while ago I managed to spin it out mid gybe, trying to do fast alpha's. Alpha's here in OZ land are GPS timed runs including a gybe, lots of fun. Infact, as I found out, very challenging when trying to push a wide arsed board around traveling at 30 knts. So having spun it out once, I tried it again on purpose, actually isnt bad fun, when you know its coming.
In 20+ knots of wind, in chop, to sucessfully gybe a small slalom board we lean our weight as far forward as possible and really bury the whol rail of the board. The board then slices through it all and we emerge out the other side.
Now try doing that with a wide arse board, sure the rail will bury, with even more foot pressure and commitment, but due to the width, the fin will be high and dry. Once you achieve this level, then you have a spinout mid gybe.
So, I discovered 2 options:
1. Bank the board only a little bit. This works well, however the arc will most likely just fit inside a small football stadium. This is ok if you like going back upwind.
2. Contrary to small board gybing technique, bury the rail of the back half of the board and keep the nose up. This will keep the fin in the water.
Heres some footage of me gybing, slow it down throughout, and you will see even at the very beginning of the gybe, just how much board comes out of the water.
Hope this helps