Doesn't look like Oz uses PANS OPS II for alternate minima.
That's because the criteria for alternate minima isn't contained in PANS-OPS II (or I). The criteria for derivation of alternate minima comes from criteria in CASA MOS 173 covering procedure design.
For info, the alternate minima is derived by adding 500ft to the height above aerodrome on the appropriate circling minima, and adding 2km to the circling vis.
From my IFR flying days, if the wx at the destination was below, or forcast to be below, the alternate minima, then an alternate had to be planned for. The rules are still the same.
Alpha