The Science Behind Building a Bigger Upper Chest
While the barbell bench press has been shown to be the most effective exercise for overall chest development,  incline chest exercises can be useful to develop the smaller upper chest without targeting the larger lower chest. This can of interest to bodybuilders and physique athletes seeking to improve their physique.
The upper chest (the clavicular head) is a small muscle below the collar bone that consists of descending muscle fibers. Studies have shown that a 45 degree incline created greater muscle activation than a 28 degree incline. 
Another study showed greater upper chest muscle activation at an incline of 30 degrees or 45 degrees.  As far as grip width, muscle activation in greater in the upper chest using a narrower grip (shoulder width) than a wide grip (wider than shoulder width).