Yeah, because you set it up with the rear axle upside down so you can get to the perches to weld them on, so you're actually pointing the pinion 5 down. Once flipped right side up and installed, the pinion has a 5 up angle built in.
So when you say you always set your rear ends with the front of the pinion pointing down toward the ground at a 5 degree angle relative to the ground this is with the rear end upside down?