Hmm... I've now run into another problem to do with layers and priority.
Because of the direction you can move, if you position the tile in the blue circle like this, it allows you to walk through it from the right. So that the hero essentially jumps from the ground up the cliff. However, If I stop the movement there, the red circle tile won't be able to be walked behind as it's the same tile in use.
Also, I'm currently mapping the top of a mountain which requires me to have a part like this:
so you can see the panorama out the back. But we get a similar problem here where you can't walk on the edge tiles and that changing it would muck it up in other places.
Any suggestions?
EDIT: Oh, just found another issue.
I'm assuming this is because there's grass on the ledge above and you're able to pass through grass, to therefore, your character can do this.