I'm new to autotiles, but I used your ground sprite to practice. I had to remove the large stones because I failed to make them look nice in autotiles.
I put that here for who want to use it !
(I haven't tried if it matches all the other "static" sprites, so it's just a test)
Now I will try to do the same for the water and the coast, and the hill...
(the framing didn't make my task easier: D)