I've had both a large Mariposa (old Style) and now now a Gorilla, in a Medium.
I like the slight wrap over the shoulders, that I get with the Medium. Its more of a balanced carry, IMHO.
With the large Mariposa, the shoulder straps where level with the tops of my shoulders, or to even being slightly above, when carrying less weight.
I never used the (2) carbon fiber stays as it would make the shoulder staps fit or ride up even higher on me.
I now like my packs to fit with the shoulder straps anchor points about 2" below the 7th vertebrate, which is the large lump at the base of your neck.