sprucegoose, is your hypothesis that because most QF (and VA/JQ international) international flights depart Oz in the morning around 1000 with a few in the afternoon (MEL - DXB at 1615, SYD - MNL at 1255 as two examples), QF crews are happier and 'fresher' on a day flight where they might arrive at the Australian departure airport at 0815, not having had to get up at too unsociable an hour (even though on day flights the shades may often be down) whereas on the return to Oz, many flights involve an overnight sector?
Do the crews intensely dislike the latter?