Okay, you make some damned excellent and quite compelling points, Varnias. However, I think we both might be going about beating this horse in the wrong way and it just ain't getting tenderized properly. I think us skewing our arguments in the direction of reality and examples there of or thoughts on what is really feasible and not is a touch faulty (never mind the fact that anyone bringing up reality in regards to 40k too much could probably use some electro-shock therapy). From a feasibility standpoint, you are quite correct and damned compelling in your arguments. Your standpoint is completely reasonable. On the flip-side, however, my stance still remains just as reasonable to me. Liegekiller made a great point in his post; in the end, there are just too damned many variables to any given situation which prity much validates either of our stances. Likewise, in a way, I feel that a character always being able to dive behind cover (after passing his dodge test of course) or utterly failing to do such doesn't take into account that more outcomes are possible due to the myriad of variables that could be at play but are simply far too numerous to take each into account separately.
Like I said, your arguments thus far have been very compelling, but there is still one major thing about your stance which I have a problem with; it's binary. You either dive out of the way of all gunmen who have the drop on you or you're not fast enough to avoid any of them. Even if a character were faced with 200 paranoid coked up Eldar all with a clear line of sight to him (they're in bleachers or on a hill or some such), the character's one reaction is still enough to trump all of their insanely ramped up reaction times and dive behind cover before any but one could even get a shot off at the character. I realize the example is a bit extreme and terribly silly, but it's to illustrate a point and the reason i don't much care for binaries. There has to be a middle-ground, more then just one of those ramped up Eldar has to have a chance to hit our character without him utterly failing. In fact, those are the only two possible outcomes, utter failure or complete success. There's no middle-ground there, and I'm a big fan of the middle-ground. That and it dose help to mimic all those countless variables that liegekiller mentioned as existing in such a situation that we couldn't hope to fully map out in a sane way.
Because of that, I'd still have to say either imposing a -20 on the attackers BS after a successful dodge by the character or (and this option is starting to look even more attractive to me by the day) our character can negate one attack against him for succeeding plus one per DoS (like dodging autofire because, well, it is a lot like dodging autofire). In small situations with small numbers, a limber and quick fellow can still easily dive behind some cover from a couple of armed gunmen. If there are 200 coked up Eldar all aiming catapults at him telling him not to move, then he should just listen to them and not move.
From a strictly rules perspective, the other things I have a problem with is it effectively dose what a half action would have to be spent doing and, on top of that, also dose what a reaction usually dose. The common half action move rate is between 2m-3m and being able to dive 2m for a reaction essentially allows a character to be as fast or faster in reaction time then things with superhuman reaction times (coked up paranoid eldar for instance) because he or she effectivly gets their first half action right after the first guy no matter what. I'm a bit reluctant to let a reaction have as much effect as a half action and still maintain the defensive capabilities of a reaction as well. It just seems like too sweet a package from a strictly rules perspective.
@Liegekiller, I'm well aware of the psychology of the gunfight... well, that is to say I've read a lot of reports and studies done on police and FBI shootings. They are the primary reason i go for what I earlier mentioned as a total chaos approach to combat and never use maps, markers, or anything of the sort. From going over those studies (in which the tunnel vision occurs in about 70% of all officers involved in a shooting) there are a lot of even more interesting phenomena that will occur due to the brain going into severe survival mode. It would seem that distance becomes distorted, time gets all forms of messed up, vision cues can be easily misinterpreted, and hearing tends to selectively go (several officers could see muzzle flashes of the gunman's gun but not hear the shots, a lot of time, they never heard their own gun as they fired back and, in their weird state of mind, thought they weren't firing, etc).
One of my favorite reports was from an FBI agent who was caught in a shootout next to is partner. He, of course, suffered from tunnel vision but also from selective hearing loss (he could hear is radio going off clear as day and remembered all the codes being called over it but couldn't hear any of the gunshots being fired at them nor their return fire). He also recalled that during the shootout, he remembered seeing beer cans floating by his face and part of him wondered who would be in this shootout throwing beer cans in front of is face and why the hell someone would do that. It wasn't until after the incident was over and he was able to actually reflect on it that he realized what he was seeing was the spent shells being ejected from is partner's gun. His mind had just been locked onto the gunmen they were shooting at as they were an immediate threat to his life and everything else, his mind simply didn't even want to bother with. The sells were so close to is face tat, due to forced perspective, they looked about the size of a beer can and since they weren't an immediate treat to his life, his mind left them at that.
That's the feel I try to convey in my combats. I just wish the combat system for DH/RT was a bit less dice and math intensive to better allow for that kind of intensity -having to stop the narrative to scribble down some hasty math takes a bit of the tension out of the combat sails.