The problem with the scicily campaign map was that to make his heights tga he had enlarged the regions tga then edited it. Because the regions tga is half the size, this ended up with very jerky coastlines.

It is not the regions which determine the coast, it is the heights, and though the two should vaguely match up, it is not precise. So look at your map_heights.tga, where you see this (g = gray land pixel, b = blue sea pixel)

ggggbb
ggggbb
ggbbbb
ggbbbb

Change it to:

ggggbb
gggbbb
ggbbbb
ggbbbb

And your problem should be solved.