That method only works sometimes, depending on the angle of the engine/transmission.

Pinion angle is the relationship between the transmission centerline and the pinion centerline. Ideally, you want the pinion to become relatively parallel to the transmission as the pinion swings upward when the car is under power. This is how U-joints are designed to run.

In other words, make the pinion parallel to the transmission as a base-line, then rotate the pinion downward 2-4 degrees.

Don't worry about the operating angle of the driveshaft unless the vehicle is severely lowered or raised, causing the U-joints to bind.