The problem with the enemies falling through is the largeness of the model uses. As soon as a model get's over a certain size, FPSC starts to miscalculate the bounderies. This can only be solved by either scaling down the model or breaking it up in smaller parts. That's what I've done with my terrains and enemies will not fall/walk through them at all.
When making such a large scale model dynamic you will see other problems arise. Because of the collision error, the whole terrain may fall through the floor completely and dissapear.
FPSC wasn't created with large models, like landscapes, in mind. You just need to find a way around the limits and it works fine.
While such terrains may look cool, and I really like this one, they're not unfortunally really useable in a game unless you do some work to prevent the charaters from reaching the terrain.
