I know little about AAR as it was many years ago that I did the course, but an aircraft uses a disproportionate amount of fuel climbing to height compared with the cruise. Roughly an hours worth or cruise fuel. After a couple of hours airborne there would be a significant spare capacity.
Then you presuppose that the tanker will come in to the mission airspace. It might be necessary, for many reasons, that flight refuelling takes place away from the mission area. Furthermore a pre-task refuelling would then allow an uninterrupted mission rather than having to suspend the mission at some point.
This is not to be construed that there was any flight refuelling on this mission just that a top-of-climb top-up and pre-task top-up are both much more likely than an in-mission refuel. If necessary a post-mission refuelling can also take place but this would not necessarily be necessary, certainly for long-range aircraft.