Bauerfeind Malleoloc

I was wondering, the ankle brace Bauerfeind Malleoloc ankle brace only comes in two sizes. Its curves follow the precise form of the ankle, how can you ensure that when you tighten the straps (for a better fit)the form of the brace will not fall incomfortably. I want one of these “wonder” braces to play volleyball but can’t spend that kind of money on a gamble, that I can’t even return if I try it on (because that would be opening the box!).