Cx policy always requires we carry an Altn for all flights within 1:45 of destination. The airports in WA within this time don't meet the RFF requirements, so we must carry IR of 2 hrs.
There are wx minimums thrown in to the requirement as well.
A good policy I think.
This means that all Cx flights into Perth will have about 2.5 to 3.0 hrs fuel on arrival.