Genetics play a very important role. So does proper training. Lots of trail and error. Sounds kinda weird but my shoulders and my chest are very proportionate to each other. I totaly kill my shoulders twice per week. I only train chest once per week, and my chest grows equally as good as my shoulders. Trail and error son, trail and error.
P.S. - whats a shoulder routine with and Overhead presses?
Bodybuilders must do overhead presses!