Dick, those coverage diagrams are well out of date for ADS-B as there have been further outlets added recently, for instance at Mt William in the Grampians west of Melbourne and Mt Tassie in Gippsland. No idea what has been added near Brisbane.
According to this there will be 74 outlets in total in 2015:
https://newsroom.airservicesaustrali...e-surveillance
A quick count shows 28 or so outlets on those maps so a a further 45 or so need to be included. No idea if the 74 includes the Tassie and Sydney multilateration gear though.