I copied this from another site.
Angle setup for two-piece shafts is similar to the one-piece. All three working angles should add up to zero. The easiest way to do this is to mount the front shaft section so it has zero degrees through the joint at the transmission. The rear shaft may then be treated as if it were a single shaft. Sometimes this is not possible and all three angles must be juggled to arrive at zero.
Don't know if that helps you.
This is my knowledge and opinion...
The pointing the pinion down a few degrees more than what is needed comes from drag racing. With the extreme loads and axle wrap and such the theory is that the pinion angle is correct under load. I don't know if that is necessary in your application, even if you did manage to twist the pinion up under acceleration it would probably come back down once under way. You do not necessarily want the front driveshaft in a straight line from the tranny. If it is then the u-joints are always spinning the same and they will wear quicker. By adding a little angle at the front joint it helps the needles rotate in the joint therefore lubricating them better.
What is your vehicle and mods, might be able to help you out a little better.