Doors get in the way and can make it hard to enter the next room in AT and be surrounded. Someone said doors in AT were added to stop skeletons from healing each other from other rooms. If we had tiles that you cannot see the other side from instead of doors it would do the same thing and would allow the entrance to be wider so that the player can more easily walk into the room and classes with companions could have their companion get in easier to be surrounded.

I added the doors in the first few rooms to separate one room from the other.

A NoMonster flag can be set to stop NPCs from moving from one area to another. For example, these were added to the Pents to stop leading NPCs away.

We can remove the doors and replace them with NoSight and NoMonster flags.

Is that what you are after?

The monsters already ignore what is in the other room and do not cross over or spell over. The only difference would be removing the doors. I don't think it would be much of a change, and very little help as far as entering the room without being surrounded. You just need to get the technique down for entering without problems.

Or you can just stand in the door and kill 18 at a time with C2, Poison, B2.