I havent noticed a difference. I have seen many different style, and thought for sure some of the ones with less coverage wouldnt work as well, but they all seem to work just fine, regardless of the legs.
It seems to me that what really matters is the diaper under the soaker. You ideally want the leaks stopped before they get to the wool! <img alt="" class="inlineimg" src="http://www.mothering.com/discussions/images/smilies/orngbiggrin.gif" style="border:0px solid;" title="orange big grin">
I have some wool covers that I made for DD that have no cuffs at all. I wanted them to fit well under clothes, so they're really trim-fitting-- they fit kind of like a pair of underpants. The diaper even occasionally will show a bit down between DD's legs. Anyway, even with a soaked prefold underneath after a night's sleep, I've had no damp clothing.<br><br>
As far as poopy leaks, though, I think you'd want a more substantial cuff. My DD eats a lot of solids and her poop is not runny at all. With an exclusively breastfed baby, I'd worry about poop leaking without good cuffs.