(edit) Backside hull ridin' wolf-style:
There's an 8" FibreGlas GL flex in KALI, a 6'3" Liddle Musko/go. Everytime I try a larger fin, the board gets "tacky", as in a tacky substance. Things are a changin'. These smaller fins I've been using seem to have given me access to more surfaces on this board, lending a way to transition amongst the many curves and contours of the board as it moves across the wave. I started using smaller, stiffer fins at beach breaks, as a flexy, and larger fin would auger the board into critical and terminal attitudes. The smaller fins bled off turbulence and allowed quicker recovery of the board. I see why pivot style fins help hulls since the boards have such "down the line", "locked in", and "committed" contours. The pivot fins loosen things up. Well, that's true when the board is listing in a light turn. Add the surface coverage consuming half the board in a committed high speed bottom turn and the fin will be apt to do some things "of its own".
That's an extreme, but it gave me an idea of what forces are at work during high speed and deep bottom turns when you have a longer, low rake and "noodley" flex fin.
This is where the story changes. Keep in mind that I am using smaller fins in smaller boards. Paired with a wide but foiled tail, the smaller fin seems to be the ticket. Now take a longer hull that's 7' and above, I'm confident that a longer fin would then be the "ticket" as surface area and foil of the board would even the fin's "effect" out. The idea of fins "I want to use" has no meaning to me any longer.
Next "Fin Diaries".....Lalo's Red fin and the spiral vee.
p.s. I guess I should elaborate on my documentation as my observations may ruffle some feathers (why they would is beyond me). All of my writing is from a personal account of my actions to explore waves and the boards I ride them on. Every experience will be different and I sometimes depart from the familiar to attain other experiences. This is what I do, and it is not a call to arms. Hope you enjoy your adventures as much as I.