It would be useful to know the rough depth of the australian sensor.
First contact lasted for over 2 hours but at a shallow depth.
Given 3.5kn, that suggests a detection range of between 4 and 5nm and a subtended angle to the seabed of around 90 if the sensors pass immediately overhead.
It is the second pass where depth is interesting.
Detection of both pingers suggests closer range so much greater depth.
Shorter time (and perhaps a track of less than 1nm) could be largely due to depth. If the detector depth is ~2000m, that would be consistent with a range of 1nm at a similar angle. Close!
We have a much smaller area of search - also indicated by stated possibility of remote vehicle deployment in the near future (if not already out).