Further to Engines' comments:
One document I have seen describes A and C mission profiles as "hi-med-med-hi" and the B as HHH. That was old and may have changed, and nobody as far as I know has disclosed how much time in combat with A/B is included.
The published reason for ditching the tanks on the A (around 2008) was that the radius increase was small. A 2007 brief for Norway put it at 55nm on an all-high-alt surveillance mission.
The shorter range of the C is not all that surprising. It has more fuel (because of the deletion of the gun and ammo as much as/if not more than the larger wing) but the larger OEW means that the fuel fraction is a bit smaller.