I've been experimenting with Wilbur a bit lately to process a starting rough heightmap and have been having a hard time getting Wilbur to preserve some of my coastal lowlands. Basically, things behave pretty well where I have large-scale regions of lowlands near the coast; there they start out low and stay low through 2 - 3x cycles of precipiton erosion. Where the coastal plain is more narrow though (e.g. where coastal mountains meet the sea, leaving only a few pixels of lowlands), the same number of precipiton cycles tends to fill the lowlands up and create cliffs instead of a smoother descent to sea level; this happens whether I have the land selected with a mask or not. I guess my question is whether there's a way to preserve these coastal lowlands while doing a few precipiton steps, or if the best strategy would just be to manually paint down the coasts at the end? So far the only thing I've found that works is to start off by doing a morphological erode, which tends to give a uniform "ring" of low terrain on the edge.

Any input is appreciated!