Besides diameters, it also has to do with turning radius and how the rear wheels/tires follow the front through the turn, which was all taken into consideration from an engineering perspective when the transfer case was designed and matched to the drive train. A staggered setup could impact this; how much I don't know.
The rear wheels are 12.7mm / 2 - 3mm wider than than the fronts, or 3.7mm (on each side from the centerline of the differential to the outside of the wheel). I'm pretty sure this is a negligable difference but I'm not the engineer that designed it.
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