start working the clavicular head of the pec. All the incline presses in the world are still horizontal flexion, stressing the mid to lower pec. The upper pec, the clavicular head, has pretty much just one function-shoulder extension-which is a front raise, or a press with the elbows in tight to the body. Granted, you'll get a lot more delt and tricep involvement but your upper chest will finally be really stressed and you'll have a shelf up there before too long. Make sure to do your rotator cuff and upper back work though.
Incline presses are not horizontal flexion-b/c they are inclined. A flat bench is horizontal flexion.
The pec does not have a "head", it has orgins along the clavical and then insertion points in the upper arm.