Originally Posted by
izzik
It sounds like
CargoHoldFlyer has the right theory. First overwater carrier determines the fare used. QR has higher DONEx fares than BA ex-CAI, so if you choose "...DOH-BOS..." then the QR fare below kicks in. Note that this is separate from the carrier that actually tickets the booking (QF for the majority/all of oneworld.com bookings).
But then why would the base fare drop by several thousand dollars if I switch the final leg from AKL-DOH to AKL-SYD-SIN-DOH, given that they're both QR DONE4s?