This is something that comes up allot.
Even if you don't put water in your BOAB you can still get a 'wet leg' not much can be done really, some people fashion a sort of plastic patch that folds over the belt behind the BOAB so the water hits that first and not your leg.
Trial and error as with most things but I find if your applicator is not too wet and you put it in carefully that will reduce it quite a bit.
Andy