A thoughtful & thought-provoking question, Raftman. . .
. . .And I agree with the excellent feedback offered by MLeake. You're not asking for a panacea, and MLeake isn't offering one. Rather, you're both trying to wrestle with the idea of armed confrontation that may be stopped short of the application of lethal force. As such, anyone who owns a gun and envisions using it for SD/HD should be interested in the question & the possible answers.
I tend to think of armed HD in terms of a spectrum of possibilities. At the one extreme is the situation resolved by the mere discovery of the homeowner's presence, followed by the criminal's immediate surrender or retreat. Great outcome! At the other extreme is the bullet sponge--the type that Ayoob likes to call a "Golem"--who advances inexorably through a hail of gunfire like your worst nightmare. This is the guy none of us wants to encounter, and he is the inspiration for lots of gun & ammo sales & practice, practice, PRACTICE!
Most HD encounters tend more towards the former extreme, i.e. less-than-lethal outcomes. With that in mind, I understand your question is not aimed at the "Golem" situation, but at the more typical spread of possibilities. I would say that any confrontation in which the criminal assesses his possibilities and makes a rational decision is going to be influenced by lots of factors: is homeowner big & tough-looking? Determined in voice and bearing? Small & shaky? How good are the odds of being shot or shot at if I fight/flee, etc.? Can I fast-talk this person while leaving, believing they won't shoot me in the back as I'm retreating? etc. etc.
Under such circumstances, some criminals will get an opportunity to look at the gun, and may think about it. Small? big? etc. I can't prove it, but there's no doubt in my mind that the bigger the gun appears, the more lethal the BG assumes it will be. If he's open to being swayed by that element of the equation, then he may be swayed more by my hand-filling .45LC stainless Mountain Gun than by my 2" bbl. mod. 30-1 in .32SWL. If the latter is shoved in his face, it probably appears pretty terrifying, but 30 feet across the house it probably looks a lot more "beatable."
If the situation were reversed, and I rounded the corner to face a BG holding a gun, I know my pucker factor would be influenced instantaneously by all the factors mentioned above, or at least as many as I could mentally process. If I had a chance to see & mentally process "what's he carrying?", I would far rather face a .32 than a .45--much less a shotgun, much less a double-barrel 12 ga. I've programmed myself to resist, but at some point I would conclude it's better not to, e.g. waking up with shotgun in my face. Some criminals also plan to resist as their default setting, but nonetheless have their own threshold & won't resist if it's crossed. I have to believe that somewhere in those endless possibilities there are quite a few who'll run or surrender rather than face a gun that meets their idea of that threshold.
Sorry for long post!