I will give you my opinion rather than specific answer to your specific question.
1.I divide all punches,kicks,strikes to hits to the head or hits to the body/legs
2.hits to the head need not be destructive to the structure to be effective e.i. jaw-rotation knockout,blinking,stunning,distracting to help to win the fight,but hits to the body or legs must produce damage. Otherwise,your opponent would under adrenaline not be affected by it.
3.so,with your hand properly conditioned to endure hitting hard,and you hitting hard,you should just break the ribs with your right hook
4.if you punch under the ribs,go in the upright direction
5.I like to copy Earnie Shavers body mechanics...all the force in the legs and rotation of the hips go into making the shot harder...great stuff
Hope that helps! Stay strong! ,)