Can you try to set the map region on the WPSL settings page to Australia and try it again? Also try to enable ‘Force zip code only search:’ and see if that works better.
The issue with zip codes is that a bunch of numbers and letters can exist in multiple locations around the world. 2020 by itself can be house number / highway number etc. So sometimes this will return unexpected results.
But setting the map region and if required enable the force zip code option, should fix issues like this.