This is the way I do and import my terrain models, with little to no collision problems, to both player and entities:
- Create the terrain in Bryce.
- Export the mesh with adaptative triangulation(multiple triangle sizes, not just one)
- Export as 3ds.
- Re-size in Anim8or; it's much better than using the scale factor; in fact, if you use X10 it's the only way to get the objects scaled correctly.
- Convert the 3ds to X model with Entity Maker.
- Use MakeEntitiesFromXfiles.
You're done. It seems like a lot of work but it's easily done, once you get the steps right.