Don't directly quote me at anything here, this is not 'original research', I've just been given bits of information, that, despite myself not fully understanding it, I guess I should share for people to analyze:
This contains a brief explanation of most lines in the tweak files, although it is not 100% reliable (not made by me, don't ask me in case of any errors inside

). It appears to be the case that all the deviation values are in degrees, with MinDev obviously being the minimum deviation, MaxDev the maximum deviation caused by that action, and the rest being how much deviation is added, although I do not know, for example, if movement adds deviation 'per time', 'per distance moved' or whatever, let alone how much in what time/distance.
The calculation for the actual size of the cone of fire (in meters) would be:
A = 2B tan C
A = Width of the cone of fire (meters)
B = Range to target (meters)
C = "max dev" (degrees)
Again, this is information I've been given, not information I have personally dug up, so I can't tell you much more.
According to that calculation, and the assumption that the deviation is in degrees, there's some odd results that I don't understand. The higher the number, the higher the deviation, so I wouldn't know why the M4 would have a higher deviation when prone compared to standing, as that clearly isn't supposed to be the case (and I wouldn't say I'd have noticed it being that way in-game either).
Anyway, let's use a random number to see how realistic the results are. Let's use a deviation of 3 degrees (that number appears a lot), and an example distance of 25 meters. tan(3) = ~0.05?
Thus,
A = 2 * 25 * 0.05
Therefore,
A = 2.5m
Means at 25 meters, a deviation of '3' in the code would equal 2.5m of deviation. That could be realistic, seeing of far stuff deviates in-game.
Still doesn't explain how the M4 has a higher prone deviation than standing deviation...
Anyway; once we figured out how exactly that stuff works - would a number of people possibly be interested in getting a community wiki started, seeing how the guide is going nowhere and even disappeared from the site? The devs don't seem to work on it from all I know, so perhaps it might be something for the community to simply start with. That said, I myself have never been a great wiki editor and wouldn't want to 'lead' a project like that, but perhaps some of you lot have some experience with that and we should just get that done seeing how nothing official is likely ever going to be released.