Thank you, for trying to help.
Unfortunately, I can’t find this tile you mentioned. I guess you mean the “Inquisitor outside” tile map. Yes, this is the one which provide the rock and plateau tiles. If we want to create a construct like this on my screenshot, we will need either a tile containing rock in its upper right egde, or we need a rock tile, which is passable in order to place it underneath the normal plateau-edge tile. I cannot find a plateau-edge tile with also rock on it the way we need it here. If there is none we have to build it by putting a passable rock tile underneath the plateau tile. Meanwhile I tried out all the rock tiles of “Inquisitor outside” and found none which is passable. I guess we indeed need a feature like the one Deluxe suggested it here.