If you change rear suspension it will affect front axle caster. If you lift the rear suspension, you are effectively rotating the front pinion up. Or lowering the rear suspension will do the opposite. I have no idea the relation between change in rear suspension to degrees of front axle caster, maybe it's not much.
Unless I'm way off on my understanding of caster angle but I thought it was relative to the ground being the 0° starting point.
I think it's easier to visualize if you think about in the extreme like a "stink bug" stance I've heard some call it.