Raycasts from top and sets the terrain when matching a surface of an object.

This is a really good workaround for creating special surfaces for Maps, especially because collision on big detailed objects can cause extreme FPS drops ingame.

So if you encounter such a problem, make sure to use the Terrain-to-Mesh feature and then remove the collision for the affected objects. Then, try to make the Terrain that now overlaps the object to be invisible by creating and using invisible Layer Textures. This is a hacky workaround but it does the trick!