I ride a bunch of boards - 6'4 semi-fish, 6'0 and 6'2 skinny thrusters, and a 5'4 North (can't remember the model, but it's an older square nose epoxy thingy).
at the moment I've basically got normal sized thruster fins in all of them, except the 6'4 which has one of those small quad back fins in the centre position because I snapped it's original. I find this set up let's the tail release on a cuttie with a lot of power behind it allowing a bit of tail slide, and doesn't seem to lack any drive off the bottom hand turn, but I'd like to loosen it up a bit more for the kiting in the smaller stuff, say up to chest high.
Any gurus know what the optimal set up for this could be?
The bigger problem of smaller fins would probably loosing upwind efficiency rather than loosing drive off the bottom hand turn given we have the kite to help with that anyway.
My set up doesn't have the box like this (not my photo) but the sizing is the same.
A good small fin thruster fin setup is fun. I like my fins without too much carbon or stiffness so it releases. Also too much stuff see puts more stress on the fin box.
In saying that tail slides damage fin boxes, so try to do it on the lip not under it. It's be way more critical and less damage to your board.
They are big boards ur riding. I'm stating some basics. Obviously a wider tailed shorter board will have more slide. Re fins u can slide out any fin set. It's a matter of weight shifting and wave timing. The heavier u are on your feet and the smaller templates will slide more. Re wave timing.... the bite you feel right on that shallow Shorey (when you feel powered up) with the water sucking back up the wave gives you max drive. Same as on a drawing reef. The opposite when your fins will slide easily is in turbulence.. breaking aerated whitewash or onshore incoming tide when water is pushing with wave. The weight shift is initiating a strong back foot turn; then push even harder whilst transferring weight forward centred over front foot. Once you have started the slide, if you have the right fin you can control it. It's a personal choice. I'm not into templates with too much raked tip even though some people swear by them. I like fin sets when the fronts have a slight inside foil. Fannings mediums are perfect for me; new Wilsons look good to. Al merrick and stretch have great templates as well. You can demo fins at stacks of places now. Maybe whack a small set in and work up from there. If it's a quad you can ride really small rears
I watched rowdy break a fin, take them all out and still rip a while ago. You get heaps of slide like that! 
Below you can see the weight transfer.
Anyone tried speed fins, they apparently bend in order to get more drive out of a turn as they snap back into shape?
The loosest board I have tried is the cab squid launcher with quads, not sure why but the location of the larger fins close to the rail seem to make the tail easy to flick around while still holding upwind ability (not pimpin, but seems like ideal setup).
Nothing to do with changing up your gear but having your back foot hard up against the very back of your tailed makes a massive difference when sliding the board. Having a bot of kick in the tail also helps.
