Settlement Plans questions for CA

Hi,

I've been spending many hours tinkering with the settlement plans, most specifically with the overlay and underlay models. Here's what I know so far, please correct me where I'm wrong:

underlay.cas - this deals with the direct geography of the underlying ground.
overlay.cas - this deals with the texture which overlaps on top of the underlay.
ground_types.cas - this provides the actual road paths, which are not on the texture in overlay.cas

Some questions: why do you need the "outline" in underlays?

Which of the two above serves as the actual ground for troops? My tests have shown it's the overlay, contrary to expectations.

What should be the relationship between the underlay and overlay ? If they should have all the exactly matching meshes, then I have some weird problem because even if I make them have matching meshes, the overlay has some serious clipping bugs.

Is the pathfinding CAS only useful for AI, and if so, then what is the best way to limit where inside our settlement plan the units can and cannot go? We cannot edit BPI files, so we can't create new unpassable mountain sides. What's a good solution?

To have any of these answered would be greatly appreciated.

I seem to have generally resolved the overlay/underlay clipping bug. Though the two meshes seemed identical, actually one point was a few pixels off, which apparently makes a big deal. I still would like some general info about overlay/underlay, if you could provide some; i.e. I'm still getting some unusual clipping, i.e. when I zoom out the 'level' of the overlay (the transparent texture on top of the underlay ground structure) seems to rise, but when I zoom into the ground the overlay seems to be lowering with the camera.

And one final but veeery important question: what is the best way to make certain sections of the map impassible? Like, if I want to make a Hill one side of which I want to be an impassible mountain cliff, and the other a gentle incline, how do I make the first part impossible to pass. I can make one side steep and the other sloping gently, but the soldiers will walk across one as easily as across the other.

The way this was done in Vanilla was - well it wasn't done really because there were no impassible inclines, or any inclines at all (in the cities at least). What were impasssible were the buildings. So aside from creating a separate CAS for every little custom nook and cranny on the map, which would be a nearly cyclopean task, what other solutions do I have to limit where the soldiers can go (without using buildings)?