I think it is an interesting question.
However, my personal belief, which I’ve flogged to death on here probably, is that physical size often means very little. For example, I am 187lbs, and in clothes I look like a lawyer, more than a fighter. I am not intimidating in any physical way whatsoever. You say that 240lb bouncers are scary. For me, one 240lb guy, whoever he is, however good a fighter he is (including MMA champs etc) just isn’t that scary. Not because I’m billy badass, but because one on one you can always level the playing field with a weapon, or get out of trouble. One on one should ALMOST never be scary, because superior tactics and street smarts can prevent you being on the receiving end of a beating.
Bouncers are scary, because they work in teams. Multiple angry 240lb guys are scary, because even with a weapon you’re probably going to be the one who gets really hurt. 2 x 150lb guys scare me more than 1 x 240lb guy. 1 guy poses a finite number of potential threats, which can be effectively managed. 2 guys pose a much much larger range of possibilities, even if those two guys are little bitches.
Honestly, I have avoided many many fights, because I don’t react when people start shouting at me, other than to maintain open eye contact, and smile calmly. It sounds ridiculous, but I think composure when faced with violence can add a lot of pounds to you in the eye of the guy in front of you. I know that there are guys who are physically unremarkable, but when I’ve held their gaze, I’ve been aware that they were blokes who would take some serious beating.
Doesn’t really answer your question. Basically one bloke, by himself, can always be beaten. Being bigger and stronger is an advantage, as is height very often, as it is harder for a 180lb guy at 5’7 to beat a 6’4 250lb guy than it is for a 6’+ guy to win. No real studies to back this up, but in my experience, height is always an advantage, perhaps more than weight (as long as you aren’t just a beanpole)