Pec major carries nearly all horizontal pressing. It is not recruited the same way at every bench angle.
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Pec major runs from the sternum, clavicle and upper ribs to insert on the humerus. Its main job is horizontal adduction — bringing the arm across the body. The clavicular head also flexes the shoulder, which is why incline work loads it harder. The larger sternal head dominates on flat and decline.
The chest responds well to moderate volume: ten to twenty sets a week covers most cases, split across two sessions rather than one. Mix heavy pressing at 4–6 reps with work at 8–15 where range of motion matters more than load. Flyes complement pressing because they load the muscle stretched, which a press does poorly.
Chasing range by letting the shoulders roll forward at the bottom. Keep the scapulae retracted and depressed throughout — that is what gives the pec a fixed point to pull against.
Names are the ones the app uses.