Ah, but you are moving the link mount when you change the pinion angle. Drop the pinion, and you have just moved the upper link pivot point on the axle forward, and the lower backward. Reverse for upping the angle.
On a long WB car, this 1/2" of pivot location adjustment would do little. But on a short WB car, with short suspension links, its a world of difference.
The shorter the suspension links, the less adjustment is needed to see results.
A good example: Take a drinking straw. Loosely grip one end with your thumb and index finer, about 1" from the end. Now pivot the straw from the long end with your other hand, and note the distance the short end moves in relation to the long end. For every 1" of movement on the long end, there is only 1/8" on the short end. Now, do the same thing, only pivot the straw from about 1" away from your other fingers. now, its suddenly 1/8" to 1/8" relation.
Long links, bigger adjustments. Short links, little adjustment.
Mind you, the percentage you can get from our suspensions is only + or - 6 or 7%. But that 6 or 7% can be the few needed seconds on the track you need to win!
As for calculating the % of AS on our chassis, I have fabricated enough custom 3 and 4 link suspensions to get a good feel for it just by looking at the link locations in relation the the axle and frame.
If you want, ill dig up the numbers and calculations and get some exact figures for you.