Not the bitmap. The terrain needs to be larger in the terrain editor. Click that little /2 a couple times to get it up to 1024. Of course, this mains a large file size than you were expecting... unless you change it to a procedural terrain (which renders slower). I didn't change your terrain texture to a mix, since I'm sure that's not the problem. In my example render above, I had 3 different textures blended and controlled by maps without a problem. But it was a 1024 terrain using 512 dist maps. Btw, using higher res dist maps has a different benefit. The higher the res of the dist map, the cleaner the seperation of the terrain materials. If there aren't any closeups, you can probably get away with a very small map.