what exactly causes the actual shockwave to form where it does?
Its been a while since I looked at supersonic flow profiles, but from memory - the shockwave forms at the point on the structure where the airflow first, or just after, reaches M1.
A good reference for all of this gumph is 'Aerodynamics for the Naval Aviator', its ancient and new copies look like they are photocopies of photocopies, but the content is very good.
When I was in Uni looking at all this, someone once mentioned that a B747 wing creates supersonic airflow near the wing root at high speed cruise - can anyone confirm or scupper this rumor?