Gus, I vaguely recall noticing that myself, and it occurs to me the asymmetrical shape could be to offset torque - especially during rapid acceleration, which would also accompany a crash-dive (or emergency surface).
Note your 206A is a very small and cylindrical boat, and dive planes apparently "favoring a left turn" would in fact favor a counter-clockwise roll - thus, they could offset a clockwise torque, from a counter-clockwise-turning screw (if that's what she has).
I can imagine that during emergency maneuvers, the last thing you'd want is for the boat to start rolling over.
I do know that, on (at least) some small single (tractor) propeller-driven planes, the rudder is offset slightly (to port, IIRC) - to offset the roll induced by the twisting slipstream, caused by the prop.
Perhaps on your 206A, the bow planes also set up the same kind of opposing slipstream - in addition to their torque - to perfectly counter the torque of the propeller, aft.
In other words, I don't know, either - but you gotta admit: that's damn good for bullsh**!