Math is pretty close to right. I moved my forward 11.5" and I think I could've gone another half inch or inch. They move in an arc backwards, so I was trying to get them to the front as much as I could.

This reversal from factory helps with the departure angle, especially on a 4Runner if you plan to bob it (like I do). The downside is that it points your pinion down a little more than if  mounting the springs short forward.