It's actually the '3 foot away' stickup reason that I've considered the pocket pistol/derringer + wallet holster option.
Of course there's always the oft-advised deescalation route. Give them your money and play nice. Get nasty if they don't. No sense getting your organs perforated if you don't need to, right? I know we all feel empowered by having a firearm for carry but the reality is that what regular guy says is 100% correct. At touching distance, your reaction/draw/fire time is too damn long. They have the initiative and the advantage. Your best bet is to mitigate that as much as possible before engaging or to neutralize the conflict.
And if you do get into a conflict with a knife wielding MZB at touching distance with your weapon NOT drawn well.. shame on you for having bad situational awareness. You didn't use the weapon that mattered - your brain and it's accompanying high tech sensor suite.
That being said, your hands/feet/elbows/knees/head are almost always available and drawn - so no wasted time if conflict is unavoidable. Just get that knife under control asap and then control the attacker. Learn a go-to disarm and make yourself proficient as hell with it.
Drawing your gun will require a significant enough opening, which unfortunately will likely not present itself easily
Anecdotal story relevant:
My stepfather (side note: he's a big guy - 6'4, built like a linebacker) is a delivery truck driver. He's long been an influence in my life regarding firearms. He was delivering chips (Former Route Manager for Middleswarth) to a store in central Harrisburg. He has always been wary of delivering in harrisburg especially given how exposed he is. He kept his loaded AMT 45 ACP pocket pistol (of which I am duly envious) in his fanny pack.
As he was delivering one of the last racks of chips he turned his back to go to the van and saw a man out of the corner of his eye wearing a trenchcoat. IN JUNE.
He immediately stopped, reached down to unzip the fanny pack and put his hand on his pistol. The man took no heed and at this point pulled out a damn MACHETE. As the man stepped forward (distance approx 15 feet per his recall) the store owner interceded and said "I don't think you want to do that sonny. He's got more than a calculator in that fanny pack." The man stopped, paused, and then ran out the back of the store as my stepfather continued the draw to expose the pistol.
Draw from that whatever you may. IMHO if the man was committed to attacking, he would have done so. However, he was more interested in an easy score of cash from a delivery driver and the payout wasn't worth the risk of having several new orifices.
What a draw from this:
A - situational awareness is key, as previously stated.
B - the draw had already begun the moment he saw the criminal in the sense that his hand was on the pistol and clear to pull and fire.
C - once the engagement began (the machete came out) he was already in the process of drawing as the man spoke.
D - the offender/perp was smaller than he was but clearly felt that despite the large physical advantage that his machete was more than sufficient.
E - until a tiny little pistol became involved.