Something frictional games should do in next games.

[Shev]

well actually, its the level designers decision, the same monster might not be able to "follow" you technically, but the level designer can create a new monster behind the door if they wish

and yes the stealth and insanity in amnesia ain't perfect, they need work

or they can program the AI so that the monsters are smart enough to use doors, and do a area transition with them like how they do with a player. They do it in oblivion, and countless other games, it doesn't have to be a level design.

So if they see a player use a area transition, they should be smart enough to follow.