I'm not sure if I understand entire question but I will address the size issue in my opinion of course. I think size matters for many number of reasons weather, water temps, big fish small fish etc. But I think the jig head itself doesn't make as much difference ONLY as being part of the WHOLE bait as it is concerned . I really don't pay that much attention to the head only thinking of what weight I want to use.
I do have a recent example from the weekend, I was crappie fishing a creek and using a small hair jig I make that is 64th oz. on a #8 hook. I caught several fish just a couple feet deep and close to bank, when the bite stopped and I went for quite a while without a bite I grabbed a pole I had a 2" BG shad bait on 16thoz head and first cast in same area caught biggest crappie I had caught all morning, caught one more nice one and that was it. As I changed areas along the creek this was repeating itself. Hope that helps.