I have asked quite a few people over the years, “…why do you use wide-grip bench presses?”
And the answer has invariably been the same, “...because they stretch my pectorals more than narrow-grip bench presses.”
But in fact, they do not; on the contrary, wide-grip bench presses actually prevent any stretching of the pectorals—the pectorals attach the upper arms to the front of the chest, and in order to stretch the pectorals it is necessary to move the upper arms as far back as possible, and with a wide grip on a barbell it is literally impossible to move the upper arms far enough back to stretch the pectorals at all.
But at the end of the day, it is presses over-head, behind the neck, dips, where there is more movement around the shoulder that builds the shoulder.
If you want big boobs, do flys.