I'm not sure if we are speaking the same "language" here.
Too much backspace moves the tire too close to the leaf springs.
Too little backspace moves the tire too close to the fender
Too much backspace (imo) is ideal, you can put the tire exactly where you want it with spacers (GOOD quality ones, billet, not that cast fits-everything crap).
Too little backspace, all you can do is buy smaller tires.
I have rims with bs so bad, I can't get a tire wide enough for the rim width under my car!