Atlas Terrain problem

Not sure where to post, but this sub-forum seemed good.

I'm importing my landscape as tiles in my mission file, so editing small landscape tiles is easier and quicker then the whole map.

But, I've encountered a problem. Along two edges, the atlas terrain finishes at zero altitude, and not the altitude it should finish up, so when lining up two tiles, there is this ragged gap and steep "cliff face".

I've got my heightmap, enlarged it by 1 pixel, made it into a raw, and got the texture file, and using the standard import process.

Am I doing something stupid? As you know, it's very much trial and error.

atlasOldGenerateChunkFileFromRaw16("legend/data/terrains/Gurth1.raw", 2048, 4, 0.0138, "legend/data/terrains/Gurth1.chu", 0.8, 4);
importOldAtlasCHU("legend/data/terrains/Gurth1.chu", "legend/data/terrains/Gurth1_geometry.atlas");
atlasGenerateTextureTOCFromLargeJPEG("legend/data/terrains/Gurth1.jpg", 4, "legend/data/terrains/Gurth1_texture.atlas");
atlasGenerateUniqueTerrain("legend/data/terrains/Gurth1.atlas", "legend/data/terrains/Gurth1_geometry.atlas", "legend/data/terrains/Gurth1_texture.atlas");

Thanks!