This might be a little late, since you said in your other thread "it's almost go time", but I'll comment anyway.
Muscle acts as better protection than fat. The biggest reason, I think, for the myth that fat people aren't affected by body shots is because most people don't strike with penetration. Most people (the untrained, anyway) will hit that top layer of fat, think they got a clean and damaging hit, and move on to their next shot. So if you're going to toss body shots, make sure you drive 'em home.