RE: How to avoid "spin outs"?
Let me think about this one for a few days.
I started to "write a book" today on the overall dynamics and physics
of how you can re-balance your rig, reposition your mast foot, change your harness line positions and spacing, and change the length of your lines and boom height to get everything more balanced so you don't exert too much pressure on the fin.
But I need to go sailing a bit and try out some of my "ideas" here before I write them up.
Please be patient and I'll have a good answer for you.