And isn’t the last post the whole point - if you need an RFDS aircraft anywhere north of a line YPLM - YBAS, surely the jet would be better off coming from Broome rather than Jandakot.
I guess a similar sort of scenario would be the Challenger jets that Cobham operate for AMSA - they are spaced all around the country (Cairns, Essendon, Perth), which allows optimal coverage of the entire country. I would imagine this is the same logic the RFDS looked at for basing these jets in both Perth and Broome.
Also worth consideration is that the jet being based in Broome would also alow the RFDS to possibly cover Christmas and Cocos Islands direct.
Cheers