I think it is not realistic to plan on hitting the bone at any point from the joint at the top of the leg or anywhere along it up until the scapula is reached. Hitting the scapula is known as the high shoulder shot, not just a shoulder shot.
To me, the shoulder joint is the forward most joint. The one about halfway between the joint at the top of the leg and the scapula.
I don't know about elk, but I know from reading the posts of a deer-control shooter (who has shot tens of thousands of deer) that hitting the shoulder but not hitting bone results in a slower kill than hitting just behind the shoulder. His strong advice was to NOT take that shot and stick to behind the shoulder.
