I suppose it's possible there's a little positive caster built into the axle, and installing a thicker or thinner shim is used for adjustment. I've been doing and teaching wheel alignment for over 40 years, and it's pretty simple- - -just make the angles do whatever is necessary to make the vehicle steer and handle properly.

One thing we do need to keep in mind- - - -major changes to steering and/or suspension components often have unintended consequences where handling and safety are concerned. A lot of research and engineering goes into designing a suspension system, and a lot of the guys who tinker with a vehicle to make it please them cosmetically have little if any understanding of the physics that makes it steer, stop and handle properly.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!