It is due to cheaper fitouts. Go back and look at capex spend...

It is due to cheaper fitouts. Go back and look at capex spend change over time and specifically management commentary over the period.
The cheaper fitouts are due to landlords paying for some of the fitout- again go back and read the commentary/ listen to the calls available from those periods.
Try to align the following figures:
FCF conversion over time
D&A
Occupancy costs
Then specifically ignore the GM % due to change in allocation between GM and CODB due to shift online and offline mix and problems with costs in their DCs (which was H2FY19).
It is pretty clear if you trawl through the history...combining the occupancy and D&A is actually really good with the AASB changes as leases now come under the D&A instead of occupancy, so there isn’t much reconciling to do. It actually makes a lot of sense...

Another thing, if you trawl through the history, is that it is clear that they don’t want to shout things out from the rooftops as they don’t want to weaken their competitive position, so it takes a bit of work to see what a diamond this is.