Had a bit of a head scratch about this on the 744 - similar system but four tanks with different levels for the i/bs and o/bs. The interest was prompted by the mention of a fairly standard arrival fuel of 12 tonnes across the tanks which brought the i/b tanks down close to the MM stipulated minimum. The limit WAS intended for maintenance purposes and pre-supposed potentially long-ish running with no aerodynamic or other cooling.
Thanks to the efforts of one of our F/Os a series of temp checks were taken during approach and landing at fuel levels which were the norm. The results were (of necessity) limited but when plotted gave an interesting divergence between the i/bs and o/bs. It's not an area in which extrapolation could be usefully applied due to the small sample structure but, certainly, the temps were heading upwards.