There is no simple answer for your questions and whole volumes can be devoted to this issue. Scars formation is, as you suggested, location dependent. Extremities, shoulders, and the sternal area are well recognized as areas that procedure poor scars. Multiple topical applications are promoted to reduce scars, but produce variable results. Other important issues are poorly understood genetic factors. Applications to reduce tension along an incision line as well as topical silicone gel sheeting also appear to help.
I wish you luck in finding a product or procedure to minimize your scar. I am also looking at my options as I will be having surgery soon. I have spent time looking at options to reduce the appereance of a large scar. As far as I have found, silicone-based products seem to have the highest rating for surgery scars; as well as, many other forms of scars. I am going to continue my research, but currently I am leaning towards purchasing one of the silicone-based products.