Here's one article that would serve as a storting off point about the spinal pressure:
http://continuum-concept.org/reading/spinalStress.html
A good position for baby in any sling or SSC is knees bent and above the level of their bottom so their weight is spread across their butt instead of at a pressure point. This also happens to be the more secure way to carry baby in the sling as you're creating a pouchlike seat for the baby from which it's harder to slip or fall out.
Herding my flock of 4 kids, all 12 and under.