I think backstabbing here is an odd mechanic here, particularly since you can't perfectly control the direction your characters face.
Also, does it kick in if you try to move away from an enemy and get an attack of opportunity?
Hello,
a) Actually, if you hold Ctrl, you can choose exactly where you face, but I learnt that after 25 hours and only because someone told me.
b) Good question about if moving away means they also get a bonus to hit you.