Since you asked for suggestions, if you look at the lower right for example, I feel the borders are too strictly defined, i.e. the mask is too contrasty. In nature, you don't often have these sharp edges, as vegetation always like to grow beyond its confines. That is true for fields, dirt paths, planted borders, forest edges, streams and lakes. Human intervention can counteract this to some degree, but never completely.
I feel this is very difficult to model, as you have to vary the gradient. It cannot be too uniform. Especially difficult for these bird's eye views.
Just some thoughts of mine.