Hi as a kite, do you walk your 11 footer? If yes, it's a calf , if no, an ankle should do the job.
Calf leggies were developed for walking up and down a longboard, the idea is you dont stand on them as much because there higher up. Having said that plenty of good longboarders don't use a leggy at all. Personal preference once again. It's a bit like the recent fin discussion, everyones different, due to style, and board size and design. And the area not touched on is how you ride certain sized boards.For instance on 10-6 AA,I would always be looking to noseride this type of a board, which entails at least a 8-5" inch deep fin to hold the tail of the board in wave. A 6-5 inch centre fin is no dought going to be looser,but imho if you whant to noseride this baby you may need to perfect your helecopter manouver. The 9-6, and shorter boards are less likely to break free with a smaller centre fin. Oh I know i've jumped around a little bit here, sorry, and my comments are directed at sup performance even though i related a longboard as an example, cheers.

Rodriguez