Think your right as no matter how high the cloud and low the plane, the plane liked being on top.
I meant to add the source to my last post in case some one sees something I forgot to add. But the problem as you mentioned seems to be game mechanics.
I'll add source now if some one like to see the code for the cloud and other landscape objects. It at the bottom of the NML file called Clouds01.
Hope over the weekend make some multi tile clouds with a bit of variety and in some cases the ground tile instead of blank add something to it.
Cheers