Satchels and parcels are different beasts.  Glad it is working out for you.  Whatever has happened has caused a nightmare for others.  

Same with me too!

They are the same when it comes to the different zones.

When you go over 1kg parcel they can be cubed but the price still changes depending on the zone.

Some years ago Aust Post changed and started charging more fore rural areas.

So just the usual reply. I was going to contact them too, but obviously it's not going to do any good. 

Listings with flat rate postage are not affected; it's all of the ones with calculated postage.  

Unfortunately the generic/scripted copy and paste reply 

And they still haven't fixed their typos 

And therein lies the problem, which I just think I have worked out.

The system is calculating cubic weight costs on all actual weight categories.  This is incorrect.  Parcels less than 1kg are meant to be exempt from cubic weight calculations, unless unusual in size or shape.  

So for example, my simple diecast car is around 50g, and with my 22x16x7.7cm box, comes in around 130g total.

The postage cost for less than 250g is $9.70 tops with Aus Post standard.  
However, the system is now incorrectly calculating cubic weight (0.22 x 0.16 x 0.077 x 250 = 0.6776 cubic kg), and so is charging me (and now my customers) as if the parcel is between 500g and 1kg.

This is what needs to be fixed within eBay - where cubic weight should apply for own packaging parcels.

As it stands, it is a total mess, but should be an easy fix (as long as eBay acts upon it).  

Since 250gram parcels came back ebay have offered 10% discount Aust wide. I get 5-35% depending on the zone. My guess is ebay will be offering the equivalent band 2 discount which is 2-25%  depending on the zone and for over 5kg likely 10%.