Yep, I get that and I know that doors line up "down the middle" so that they can be seen from either side. But that's not what I was trying to achieve here.
By putting it on the outside edge, you know have a wall that is only visible from the "inside" of the room or building. Here's a better screenshot to illustrate what it achieves.
From the inside of the tavern, the player token only sees the walls to the North East and North West, which is what you'd want in an isometric game.
When the token steps outside, now he can only see the walls on the south side of the building.
Its working like I want, I just wish I could use a bigger token than "Medium" for the effect. One, I have to use a lot of them for these walls and Two, the wall doesn't extend up quite as high as I'd like, for the visual effect. But if I try changing them to Large tokens, then you get the clipping that I showed earlier in this post.
Its still usable though. I was just making sure I wasn't doing something fundamentally wrong with isometrics. And yes, I know they're still in an early stage in Maptool, but they intrigue me...