The Ready State Virtual Mobility Coach is like having a virtual Kelly Starrett in your pocket.
Thoracic flexion/extension and rotation set the stage for the shoulder to work properly. You have to clear any restrictions at the spinal level before you can really see what is happening at the shoulder and that is why they have you doing those correctives first. The fact you don’t extend and rotate will in the T-spine could be why the shoulder feels “ugly” at the spur. The lack of T-spine motion isn’t allowing for room for the shoulder to move through a proper ROM. Otherwise check through the free videos on the sight, there are hundreds or more about the shoulder.