Shoulder harnesses should be anchored as a minimum, level with, or better,
somwhat higher than the top of the shoulders. If they are anchored
significantly lower, then in a sudden (e.g., high G) deceleration such as in
an otherwise survivable crash, there is a high probability of spinal
compression fracture.

I can't cite the source of this information exactly but I believe it comes
from somewhere in my 30+ years as an systems engineer working on military
aircraft.

(One of my skiing buddies over the years was a cockpit design and
development specialist so I probably heard this bit of wisdom from him).

Dan Schaefer