Well, I guess you gotta account for rider preferences first and foremost.
A tail 16.5 is really not all that specialty, but mostly for smaller, slower moving type surf…otherwise you’d go narrower.
So underhead high preferably, but certain Cheynes have pushed the envelope a bit.
Where your back foot is placed is based on preference, rider sizing, size of foot, steepness of waves, speed of waves, and length of waves, not to leave out about a dozen other criterias.
Wings to give you a breakway point, to allow the board to pivot right from there.
I mainly preferred twin fins, right from '68, so for a board about that size, two sidebites 7" long, and a tail variing in size from 3" to 5.5, depending on needs for holding power at speed.
Some of the guys I made boards with 16.5" tails for, preferred single 12-14" sabre shaped fins, really high aspect, chord maybe 3" at the base with slow taper to the tip. They liked the smoothness and trim speeds, the quicker drops, and less pivoty feel.
I suppose if true tris were around then, we’d have a 3rd alternative.
Run what you like, it all works, but slightly differently.
Our preferences were based on surfing at OBSF, which is generally faster moving, maybe not as fast peeling after initial takeoff.