Best thing to do is get the $5 Smith "Helmet Helper" that replaces the clasp in the back with a short rubber strap. The rubber part grips the helmet so that the strap doesn't slide around:
I think having a split strap with the clasp is the dumbest thing Smith has done in years. I really don't see a benefit to it, and in fact it can cause the strap to come undone when slack (especially with a helmet) and let the goggles fall off. It also doesn't conform to the curved shape of most helmets very well. I swap them out for the HH right away.