When I did the exercise, to see what my tank held, it was at room temperature as the bike was in a heated garage. You filled up, presumably, from a Filling Station where the fuel would have been colder and therefore you would get more in. In Mongolia the fuel is, quite often, stored above ground and is therefore warmer. The capacity of the tank will be less with warm petrol.
The MotoGP teams store their fuel in a freezer before filling their bikes thus allowing more fuel into their restricted fuel capacity bikes. As seen on the BBC MotoGP prelude last weekend.