How do you regenerate the Landscape Collision, as its not matching the terrain

Basically I need for Landscape to be low resolution, so to speak, at LOD0. I am not sure how i can do this from heightmap - it always seems to get generated at full resolution.

Meshes are great, but at 100 km^2 it needs to be modular and that creates another set of unsolvable challenges. In fact, that’s what i already have, but because of those issues with meshes i am looking into Landscape.