Thanks! Yes the outer corners which would fit between those gaps making it a smooth hill. These would be the NE, SE, NW, SW corners. This tile set has them https://opengameart.org/content/isometric-64x64-outside-tileset along with the inner corners if you were so inclined but the out corners are more important IMO.
Now that I think about it I actually wanted to prototype an isometric game with slopes that were half a tile height. So right now these slops are 45 degrees but you could also make a slope for the half-height tiles this yielding a more gradual slope. One reason for this is you can actually see the surface on these back side slopes which isn't possible for the 45 degree slopes in isometric projection. Hope that makes sense. :)
