"Not quite, that is an extreme exaggeration. The sights are only about 2.5" above the barrel, so that is the furthest distance that the POI will differ from the POA in those first 30 ft. If you are aiming at the nose, the lowest you will hit is the mouth. There really will not be a big enough difference b/w POA and POI to make a difference in an HD situation."
You're absolutely correct. I was pretty darn tired at 2A.M. when I wrote my last post, so I was just trying to crank out some words. However, they ended up slightly exaggerated. The only thing different from what you're saying and what I was trying to say is that the OP stated he would most likely be firing "within" 12ft. So, again, you're correct about the general height of the front post, and I also agree that that is the only height difference you would make between POA/POI, but I would disagree that if you were to aim nose that you'd hit mouth. It's probably more of between the eyes to hit the mouth, but that's being extremely nitpicky, which I don't mean to be, but again, I completely agree with what you're saying. I did exaggerate.
Also, to the OP, I don't know if this has been said already or not, but if you do buy a left handed model AR, you'll have killed a lot of resale value. It's hard enough to sell an AR as it is because most people see it as "If I buy a cheaper gun for now and like to shoot/hunt/etc., then I'll get the expensive gun later." Now those people will be paying a couple of hundred dollars MORE than if they just bought the expensive gun to start. That, and the fact that a good 85-90% probably are right handed, so selling a left handed model, you have scenario 1 to deal with AND you have to sell to the 10-15% crowd (which could be hypothetical numbers and could be +/-) from scenario 2.