Seems like 9/10 questions that i ask on here have something to do with fins.

This is a question that has been bugging me for a while now, and thus far haven't found an answer (a great surf craft designer said he'd tell me all about it over a beer one day, but i haven't had the time to go catch up for said beer).

Theoretically, much consideration goes into designing a fin, right? At least some times (i've got some fins that would perhaps suggest a lack of consideration).
Rake, flex and foil etc are all designed with hydrodynamic properties and characteristics in mind.
Then we have beautifully designed boards, again with bottom shapes/contours made with the flow of water as a key (only?) consideration.

But then we have a big arsed fin box. Unless the fin is positioned right at the leading edge of the fin, there's a lovely big hole in the board, right in front of the fin. The gap in the fin box prior to the fin has to produce a bubble trail. The bigger the gap, the bigger the bubble trail?
This has to effect the flow of water past the fin to some extent. Perhaps only minutely. Perhaps considerably?

Similarly, empty fin plugs are going to throw bubbles right down through where we're wanting water to exit most efficiently.
(on that note, one can buy 'infills' for unused plugs, but they don't seem too common - maybe only for over-thinking, under-educated fools like me?)

Then there's those 'adjustable' fin screws, with a lovely tab on them so that you can adjust by hand.

So, think of a board with empty side plugs, running a single fin set right back in the box, with an adjustable screw so that the fin can be adjusted in the water.... That's got to be somewhat of an hydrodynamic nightmare.

Somewhat different ballgame, but i can't help but think of props on boats and the loss of drive if they cavitate.

So my question really comes down to this - why all the carefully foiled fins and bottom channels if we're going to start throwing air where water should be?

And as a complete secondary Q, why not 'spacers' to fill in the gaps in our fin boxes, or at least reduce them?

(Again, this might be the simplest question ever asked on this site, but it's been bugging me for ages!)

Cheers!