Bigdog, I hear ya, no sweat. Most racers won't need to know all the technical terms and exactly how or why they work, it is much easier to just run a set up from someone with the time for testing.
I will say that SAI and castor are seperate though, since for example, moving the king pins inboard(only one or the other) would effect SAI, but castor would be the same.
Your right about the carpet vs asphalt, but the same principals apply, regardless of the surface. The reason the castor can be the same is because other things are done to lessen the chassis roll on the higher traction surface. Things like anti dive, stiffer springs and oil, anti-sway bars etc. This is why off-road cars have 25-30 degrees of total castor, but on road cars have 0-6 usually, since there is less chassis roll in on road cars. Castor is still used to help keep the tire in the best contact with the surface, but less chassis roll equals less castor(less SAI needed).
You probably know this stuff, but it may help others understand how it works by posting it?
After 25 years in the auto industry and 20 years of racing(toy cars and fullscale) i've been a little to into all the whys and why nots for a while, but I still am missing the time to test for myself lately, LOL.......Jim