East/West glow has been proven correct retreating procedure by my own experience.
The player cannot, however, retreat to the glow directly behind them ("south" of them).
This doesn't stop the NPCs from retreating from any glow they please (most notably their south glow/your north glow- directly behind them)
So yes, while you must retreat to only the SIDE of the map (with this being not at all intuitive) the AI can retreat anywhere they please.
If you have entered a glow, and you didn't automatically retreat, then you simply entered the WRONG glow. Also, only champions can retreat of course.