Pinion angle question

I just took some measurements and the perches are at about 5 to 6 degrees the front being upward so at this couldn't I just set the pinion level at zero. That would be the same thing as the perches being level and the and the pinion being 5 degrees correct? Or am I thinking about it backwards?

The problem with that is, "where" are the leaf springs? Are they at full droop? Also, is the frame of the car level? There are way too many variables IMO to do it in that way.