Hummm... of what part of the ground?
If it are the one that we see on screen shots, I have of to level the ground to stick on the navmesh, but you are certainly right it does not make rather natural. That said, I do not really plan to redo the map, I had make all the ground manually... but for the next map I have to use L3DT it will seem more natural, finally I hope...
PS: I can not see the img(http://img158.imageshack.us/img158/5116/tysig2lz4.gif) of your signature...