DavidJohn said..
It's a personal thing.. Personally I prefer a calf cuff because I hate standing/tripping on the leash but once it gets to head high surf I swap the an ankle cuff because I prefer the stronger tugs being on my ankle rather than knee.. Plus in bigger surf there's a bigger chance of a short paddle on my knees and calf cuffs chaff when kneeling.
+1
Was a bit surprised to hear you getting pain in the ankle if you're in Vic and have a 4mm wettie + fat 5mm leash strap? Everybody's body is different I guess. I'm pretty useless so spend a fair bit of time with a board pulling me under in a misread set but I find it much more comfortable being dragged by the ankle than the calf in bigger surf.
Exactly what DJ said though, if you're in smaller waves dancing up and down your 10'6 then it's a lot more comfortable swapping to the calf and not having the arse end of a leash tripping you underfoot.