[crunch]

The problem here, I think, is that you don't have your LOD set to 100% triangles in Radiant.
If you don't have it set this way, your terrain is not where it appears in Radiant.

To check, in the toolbar go to LOD Terrain, and look where the check mark is in the dropdown window. If it is not by 1 (100%) triangles, then click there to set it that way.
Now when you make your terrain in Radiant, that is exactly where it shows up in your map.