I actually haven't looked recently, so I'm probably wrong.
But, I'm lazy, so I'll speculate. I bet if you look at the geometry of the front suspension, you'll see that if you move the A arm up and down, it moves about twice as far at the wheel as it does where the shock is mounted. Therefore, to lift the truck 1" at the wheel, you'd only have to move the A-arm down 1/2" at the shock, which is where the spacer goes.
I'd draw a picture, but it would probably make things worse. Go stick your head under your truck and have a look.