I recently booked a Qantas classic reward flight travelling on Emirates SYD/DUB/MXP - I am travelling exactly the same route in each direction and not taking a stopover either way. I had to book it as two one way trips as the return flight was not available initially when I booked the flight over. The fees/taxes for a return trip are AUD 552 whereas the fees and taxes for the two one way fares add up to AUD 721. My understanding is that fees and charges should not vary according to whether the ticket is booked as a return or two one way trips, so I don’t understand why they are so much higher in this instance. I queried with Qantas who advised that they are calculated by the computer, so must be right! Any advice would be much appreciated.
If you are talking about the taxes and surcharge, it is related to your initial departure point.
I had a quick look on Google Matrix. By looking at the cost break down of the Emirates flights, the 2 one ways include a carrier surcharge (YQ) when departing from Milan.
If you booked as a return from Sydney, the YQ would not be included.
One way of avoiding excessive surcharges is to depart out of cities with lower taxes or countries that do not allow surcharge. Some examples are NZ or Hong Kong, Phillipines or Brazil.
Sometimes to get the redemption, making two separate bookings is inavoidable, in my opinion.