Thanks for your quick responses. I am not looking for jibing lessons and I know my technique can be improved upon.
With the 38cm fin, the spin outs occur occasionally on the jibes and if I am heading up a bit into the chop.
I am working on my "lay down" jibes (sail raked back and sheeted in),keeping the pressure on boom/mast, knees bent adsorbing the bumps. When I spin out, it occurs just before the midpoint of the jibe, shortly after I sink the rail and begin carving. The fin spins out towards the center of the radius, which turns the board away from the direction I want to go.
Your point about the wider tails must be the issue, since I now recall a few spinouts on my formula boards mid jibe. Rare, but it has happened.
Practice makes perfect so I will stick with it.