I had time to do a bit more work on this hex map project, so I picked a large hex to fully map out with smaller hexes. I started on the coast, in one of the mountain hexes, to see how things turned out. Instead of using a random pick I started in the center of the hex and worked my way out from there. Because I was treating unfilled small hexes as the containing big hex's terrain type, the small hexes were fairly homogeneous until I got to the edges and started considering bordering hexes too.
As you can see, mountains overwrote most of the original hill terrain, making this a pretty rough coastline. Small patches of woods and a few more open areas along the coast popped out, along with a small wetland on the northwest side. In retrospect I probably should have treated the mountain results as hills, since that was the base terrain for the big hex, but I think this looks fine. I think I'll work through a few more hexes to the south before I focus on my planned settlement hex, either the scrub area or light woods next to that little jag in the coastline.