Nissan Patrol 4x4 (Africa)

I am wondering if anyone can tell me why the left rear window is smaller than the right??? The support column between the rear windows and the rear doors are different widths, but for what reason?

I think the air ducting to the roof air vents runs up that broad pillar on the left hand side (the rear aircon unit is also mounted on the left behind the rear wheel).

Thanks Gerrit