Ok I did some digging. It looks like the 3* is not a fixed angle. It depends on the suspension. Ladder bars being most rigid, require 1* down. Four bar 1.5*. Leaf can be as high as 7* down. This is to compensate for the tendency of the pinion to rise under hard acceleration, maintaining the overall pinion angle at zero or less.

It is nasty mojo for the pinion angle to become positive.

Relative to transmission of course.

I hope I regurgitated that correctly.