Well, having learned about the technical names for some of these injuries, I stumbled upon this article which describes, in lay terms, the various injury types.
Interestingly, they make reference to the cranial vault-brain dimensions that I was trying to figure out earlier:
In the subdural space is the cerebro spinal fluid. This fluid performs a number of functions, the main one being to protect the brain from impact concussion. The brain “floats” in the cerebro spinal fluid, lessening the weight on the base, and is supported at the base by the spinal cord. The brain, buoyant in the cerebro spinal fluid, can move within the cranium to a very limited degree. The space between the temporal bone and the brain is only one millimeter.
My earlier back-of-the-envelope calculation which yielded a gap of 700µm wasn’t far from the truth!