I've read that stealth mode doesn't work while you're in the line of sight of an enemy. But I've found that you can't go into stealth if you're being targeted, even if they can't see you. I've gone behind closed doors and tried to hide, but the monsters homed directly on me anyway, once they got through the doors. I've heard it has something to do with being targeted and not being able to hide, go invis, use sanctuary, or anything else like that.
So, if you're being actived pursued by a monster intent on spilling your blood, can you still hide if you have Hide in Plain Sight?
DHF