Strange!
Pricing via the EK website a Christmas LHR to OZ and back, departing 18 December, to Melbourne, starting back 11 January from Brisbane. Whole trip in F.
The straightforward return as above comes out at £7283.59.
I decided to add on a circa £100 short hop on QF in Y from HVB to Brisbane and the price becomes.....
£18,882.19
Yes my typically <£100 add on ups the price by £11,600.
And strangely.....the cheaper return flight nets me 45000 Skywards miles and tier miles (not including my status bonuses) whereas the expensive version gives me 32,500 of each!