With the now warmer temps (and presumably the disappearance of winter-blend fuels) I've seen a spike in my mileage (under like conditions).
Whereas I was mostly in the 22-24 range for most of winter, my current tankful (with 200 miles on the tank and reportedly nearly 100 more left in the tank) I've been averaging an indicated 27-28 mpg. If that bears out through the calculations at the end of the tank that will represent my best tankful so far, but I expect it should continue, especially into summer months.
As a matter of fact, the Owner's manual and one automotive blog on the matter specifically say the opposite - i.e. that in BOTH AWD-V and AWD that "distribution of the torque to the front and rear wheels changes automatically [ratio; 100 : 0 (2WD) ---> 50 : 50 (AWD)] and distribution of torque between left and right wheel of rear changes automatically".
I believe the only difference between the two modes is in the amount of torque which is vectored side-to-side on the rear wheels. That in AWD LESS torque is vectored side-to-side because doing so (throwing more torque to the outside rear wheel) in more slippery conditions can actually hurt stability.