Greetings
I am the GM referred to in this scenario, and I have in fact competed in team combat and group melee.
Thus taking away from life experience I have allowed my players to perform sneak attacks while flanking.
As I see it the person standing behind you is not in sight and thus not visible or *invisible* and therefore gets the same bonuses.
yes I do indeed understand that you are not rock'em sock'em robot fighting and not standing still, but neither are they.
The term flat footed was used, but not by me.
note : they snakes where Adamantine Cobras so they nom through plate armor.
but yeah, half the system we are playing is home brew and facing is a thing, not a big thing, but still it adds some feel I think.
the question is : are you having fun and am I having fun. I got a list of yes' so far and some ? but that's it.