The whole reason for the 2 centre policy is disaster recovery. They'll never move the Aust FIR into one centre, all of the eggs would be in one basket.
Spot on!! and no particular secret from the time of the original development of the two centers.
Either center has to have the capacity to handle the whole AU FIR. In recent years, terrorist attacks have probably been added to fire or other disasters as a reason for two well separated and self contained facilities.
Tootle pip!!