Yes this is an example using that tileset this was just the one I was working with at the time, others I have do do not have inside corners, and the principal applies. Quick example of some stone pillars Since they are not natural they would not have inner corners.
It seems like it would make sense that as you mentioned, if the rule isn’t found it would include the center tile. The other issue with copying the center tile in this case would that it would prevent flood filling of the center as technically the inside corners would be different tiles so you’d have to manually change update the inner corners after the center.
I do wonder if it’d be “easier” to instead of drawing the shape, assign the role of the tile more similar to how like wang tiles work, but while being able to mark a single tile as “this is both a corner and inside corner” or something.
This would also allow for a couple new tiles that I don’t think are possible right now such as integrating a 1x1 tile into the terrain brush so the terrain doesn’t have to be minimum 2x2 to work. I do get that you could always just switch to a tile brush, but this would make the workflow for terrain a bit faster if configured this way.
Similarly this would enable single tall or single wide tiles.
Anyway, thanks for the help that makes some sense now, for now I can just use a copy of the inside for ones that it doesn’t work for.