5 hours ago, Laz Man said:Could you draw a picture or create what you are referring with the missing space?
Unless I'm mistaken, they are looking for the same block shape as a 1/4 Cube, but with the correct dimensions to match the upside down 3m Tunnel Inside Corner. That square edge on the 3m Tunnel Inside Corner is not the same size as a 1/4 Cube or a Post, so if you use those, you'll end up with a visible "lip" where the two meet. So something the same dimensions as small square edge and 1m tall so that that small square edge can be made into a "post/pillar" all the way to the floor.
In that screenshot posted above, that reddish block would have another block below it that continues the shape down to the ground. That's currently not possible except with a single shape that has a curved look to it because it's meant for doing a tunnel rather than a straight post.