The S-straps on my pack work as follows:
They curve away from my neck (1st half of the S), which is probably mostly a benefit for large necked men, but are solving a problem that would not exist if the straps were sown to the pack far enough apart. ie: sown on wider apart for large, than for medium packs.
They curve away from my armpits (2ns half of the S) for easy arm swings with no binding in the armpit. This allows wider straps at the top, without armpit rubbing, but is probably an issue for busty women, especially if they tighten the sternum strap, which pulls the straps further toward the center (even when the sternum strap is worn high, a few inches under the collar bone).
I'd go to REI and look for a pack with extra curvy straps and see how they feel.