The weird brown tiles have a -15 altitude to propertly display a water border tiles - water static wave tiles will be created at locations of that brown tiles, and considering that that the coast basis lays on 10 altitude points below, wave tiles will lies above coastline tiles. But if brown will have -5 altitude, the altitude of coastline become equal to water border tiles and be overlapping them (in fact of their upmoving from -5 to 0, so trouble will be the same. So it's not a solve of trouble.
Let me explain more clearly on a graphic:
At First image i have draw the original dragon coastline construction method. Brown tile transtiting with a grass creating a coast tile that upwalks from -15 ( brown tile level) to 0 (grass level) above that coast tile is water edge tiles are placing. In fact of that a most of coast tile mass is below water edge, it's overlapped by it.
At Second image you see the trouble that you encounter. Very high grass level with low level of brown tile generating very sharp raising coast tile. In fact of that the very most of the coast tile is above the water edge tile, it lies ABOVE it and overlapping it.
At Third you can see the method you are explained in that topic. Shortly, if you raise up a brown tile to level of water, it with a grass will generate a coast, which will also have a water altitude level, and overlap it Totally.
That a point...