Ok If it's right or not, this is the way I see it. Pinion angle is not going to give you big gains in traction only small gains in freeing up friction in u joints and pinion and trans tail shaft bearings. What I hear it would be a stretch to get 5% gain over badly matched angles. If you was to draw a straight line from tail shaft to pinion, use that as a base line and try for even amounts of difference on each end. If pinion was 2 degrees down from that line, you would ideally like tail shaft to be 2 degrees up. You will generally get a little movement in a ladder or 4 bar so if you have a little more down it will take the slack up under pressure. You do not want either u joint with no angle because they can get bad harmonics. From not rolling them little needle bearings it will cause premature wear and loose joints. The harmonics are transfered into pinion bearing and tail shaft bearing causing premature wear also.
The Idea that there is a magic pinion angle came from the days of leaf spring cars and pinion snubbers. The pinion angle then could determine your anti squat line depending on how fast or slow it hit the snubber. If it hit it fast your front part of spring didn't wrap into an S so bad and changed the angle between contact patch and front spring mount. Maybe a little more complicated than that when you start moving snubber also.
Hope that clears it up.