I think you're on the right track about larger fins benefiting from a larger base component. Also, it's important to keep in mind that fin box systems must be structurally integrated with both the bottom and the deck of the board. As the thickness of higher volume boards grow, the fin cavity area becames larger, thereby increasing the bearing surface potential. But I think that the greater width of boards over the last 10 years or so has mandated the need for larger fins to properly balance the equation. With the huge leverage that large fins put on the finbox structure, it just makes good engineering sense to beef up the fin base to spread out the overall stresses involved.
Still, as you correctly noted, one can still use a standard tuttle base fin in a deep tuttle box. I think that the way that deep tuttle boxes have been structurally engineered, the design can accommodate the standard sized tuttle base fin. However, all things considered, I think there are certain limits. For instance, I feel it's fair to say that a 70cm fin truly needs the deeper base to avoid undue stress on the box structure. Yet, I seriously doubt that one could find a larger fin (50cm and up) with a standard tuttle base, or a Powerbox base for that matter. The design of the latter finbox configuration just isn't sturdy enough to handle the leverage forces that larger fins impose.
Last edited by steveC; 13th January 2008 at 12:46 AM.