This is a question out of curiosity as googling does not find me an answer.
Looking at an itinerary of AKL-MEL-LAX as an award ticket redeemed with Alaska Airlines miles, I notice that if the MEL connection is on same day, the taxes AS charges would be USD53, which already includes the 3 US government's taxes, as
US APHIS user fee $3.96, US Customs user fee $5.65 and US Immigration user fee $7.00, total to $16.61, as well as $12.50 partner award fee, with the remaining $23.89 presumably from New Zealand government.
However if the same itinerary requiring an overnight at MEL, even it is less than 24 hours, the taxes jump up to USD136! The portion collected by US government should remain the same at $16.61, so as the $12.50 partner award fee, and the $23,89 New Zealand departure taxes, so Australian government charges $83 for an overnight but LESS than 24 hours transit at MEL? Even the notorious LHR APD does not apply to <24 hours transit. That is quite a hefty tax charged by Australia government when the passenger is just transiting Australia.
Could someone enlighten me, as to whether the tax calculation is correct, or AS system has mistakenly calculated the correct taxes to charge? Or it is indeed, regardless whether you are transiting or you have a real stopover, Australian government would collect hefty taxes on you?
Direct flight SYD-LAX the amount is $101, which includes $16.61 US taxes and $12.50 AS partner award fee, leaving $71.89 from Australia government - that is on the high side among airports worldwide. When there is a connection, things get puzzling again.
SYD-MEL-LAX, same day connection the total taxes come up to $107, and an overnight connection is $111. Why such difference?