I was just browsing through some images of people with proportioned pecs and found an awesome real life representation of the upper pecs compared to the lower pecs. The author of Scoobys Workshop seems to have the two muscle groups figured out. Here is the link: http://scoobysworkshop.com/2012/04/21/upper-pec-lower-pec-chest-exercises-for-mass/
Upper Pecs and Lower Pecs
Doing incline bench press before you do flat bench can greatly help you increase the size of your chest. A lot of people do flat bench and neglect their upper pecs. This causes a dis proportioned chest. What ever of the two workouts you are weakest at is what you want to start with at the beginning of your workout. A general rule of thumb I follow, no matter what workout I am doing, is to start with your my weakest areas. This will help you proportion your body and sculpt it to your liking.