Maps of the Indo-Pacific are usually oriented around the first island chain as a barrier. Looked at from the south, the same archipelagos read differently: as depth, as warning time, and as a set of partners whose ports and radars matter more than any single platform purchase.
Depth is a relationship
Archipelagic depth is not something Australia owns; it is something its neighbours extend or withhold. That makes diplomacy in Jakarta, Port Moresby and Manila a military capability in the strictest sense.