Reading On Killing and On Combat the author makes a great deal of noise about how small a percentage of people will kill someone they are looking in the eye at close range, but how many more will shoot the same person in the back at the same distance.
Funny, I just finished On Killing and am reading On Combat and I don't see where he's "making noise". I do see a lot of well documented research and surveys of combat veterans, though. I also don't know where you're getting "many more will shoot the same person in the back at the same distance". Must have missed that part.
What I do remember clearly is that in WWII, a small percentage of
riflemen fired their individual weapons while in combat, even when the enemy was clearly visible. A much larger percentage of gunners on crew served weapons fired at enemy troops, probably because they were more accountable due to being part of a crew.
That was changed in Korea and Vietnam by changing training methods from shooting at bullseyes to shooting at human shaped silhouettes and applying the principals of operant conditioning, thereby overcoming the natural hesitancy to shoot at fellow human beings and increasing the rate of firing individual weapons to 90% or better. This was done without regard for the consequences of what happened to those folks
after they pulled the trigger, but the Army wasn't terribly concerned with that at the time.
I don't think he made too much of an argument about "shooting in the back". IIRC, his analysis involved the role played by physical distance in killing, everything from artillery range to bad breath distance.
If I understand your question correctly, I believe that turning your back and running would prompt the predatory nature in most BG's into attacking. I agree with Rob, don't turn your back, mainly because it's better not to lose visual contact with the BG.
I learned this a long time ago. Flinching and closing your eyes doesn't make getting hit feel any better. Best to keep your eyes open and focus on the threat.