I don't think this is a good idea, or necessary, or the best way to do tactical strategy.
Just assign hit percentages to body parts, if they don't hit, oh well.
You don't even have to do what you're proposing, all you have to do is to ask "this body part is within 1 feet of this other body part, which means there's a corresponding amount of chance to hit another body part. No fancy cone based calculation necessary.
If you really want to be 400 IQ and intelligent, what you should really be thinking of, not just "what body part I can hit" but instead of that, organ modelling, and body part modelling like "I want to hit the bones of the arm" or "I want to hit the knee", which would obviously lead to vastly different results.
Also create accompanying conditions, due to, for example, bullets hitting a knee, bullets hitting a leg bone and shattering that leg bone, bullets not doing any of the above and only hitting the muscle, bullets grazing the skin and fat layer which should be mildly uncomfortable but otherwise alright, bullets hitting the eye and disabling or limiting vision, bullets kicking up dust that can go into the eye without adequate eye protection...these are the ideas you should be thinking of, imo.