
Lifat |
RAW there aren't any facing rules so yes, you will be able to see the entire battlefield. It isn't that unfeasible though either, because unless you are an army who knows attacks aren't coming from behind you would also check your back periodically. This is why flanking exists. Once you are flanked you can't react efficiently against both attackers, so they get +2 to hit AND you count as a sneak attack target.

Umbranus |

It is quite easy to change your facing several times per turn and as such it seems to be just simplification to ignore facing.
That it doesn't matter from where an attack is coming doesn't mean that you see 360° all the time. Only that you are able to turn your head to remain aware of all opponents.

wraithstrike |

Yes you effectively have 360 degree vision. The game simulates this not being true with flanking, and by giving some monsters "all round vision".
Short version of a rule->If you can draw an unobstructed line from any corner of your square to any corner of another creature's square then you have line of sight, and that creature can not hide from you while it is being observed.