From my personal anecdotal experience, I've found it worse when travelling east around the globe. I also tend to stay awake most if not all of the flight, so sleeping time doesn't tend to matter as the flights from London to NZ are minimum 28 hours. Shorter flights you can arrange around daylight hours to reduce this, but otherwise, there must be better strategies to help out with the tiredness/not sleeping.
So I was fine despite nearly 48 hours of non-sleep from Mongolia to London, up the next 3 days at 8am to do stuff. However, the second week has been awful, sleepless nights and erratic sleepiness. Any theories?