I would have thought it would also have been to keep the guys behind Hamilton behind. I dont think that cooling would be an issue, as the cars sit on the grid for a while before getting off, however, the stationary pit stop time would be the critical difference, as going in straight behind Rosberg, he would have lost time through sitting still, at least if he drops back, the guys behind him will be the same distance behind him, regardless, and there would be less stationary time in the pits, so the track time lost to those behind him would be minimised, 6 seconds I guess is the time the team calculated, with an eye on all the other key players at the time.