The bolded part people tend to overlook when talking about "balance" vs setback.

Pull the seat back and lean forward more, you might have more weight on your hands. Straighten your arms instead, sure you'll have less weight there. Yet how much your core works to hold up the torso weight makes more difference in weight on the hands than the saddle position.

The saddle is also a pivot point, and in that respect reach and torso lean are the operative factors (rather than saddle setback dictating).

I tend to agree with [MENTION=183557]rpenmanparker[/MENTION]'s point: if you're talking about positioning for weight balance, you have to begin with the actual desired weight distribution. If there is no quantification for that, for whatever type of fit is desired, it means that physical weight balance is not what's really being adjusted. Which is fine if a fitter is just using a simplification to explain what he's doing - it doesn't really matter if the explanations are wrong as long as the result is acceptable. But it sure can lead DIY fitters down the wrong path when they take these incorrect physical descriptions literally.