Sorry mate, but you don't have to give a reserve selection for every race! You're supposed to pick a couple of reserve selections from ANY races in Australia. They don't have to be the same races that you got your four top selections from.

Think of it like this. In the feature race, you pick your top selection and a reserve. Then you pick the best 6 selections from all of the other races on the day. And you simply choose the best 4 of them as your top picks leaving the other 2 to be your reserves.