Hi Burr, it's not particularly an "error" to have large underlying surfaces, it's a valid way to have geometry constructed.

If you like you can run the ShrinkTrimmedSrf command to reduce them.

I was a little surprised that the segment pieces were trimmed extended cylinders instead of ruled surfaces (like loft between 2 curves) but either way is valid.

But the ruled surface way would probably be a lot simpler to code because you can make something like this in just one use of the Loft command with Loft style = Straight:





That Blend behaves differently on the edge of a box versus the edge of a pipe3 elbow segment (because they are not isoparm edges) is more of a limitation in Blend where it is trying to automatically adjust behavior so that it doesn't pop up a huge set of options.

But it would be useful to be able to control that behavior in Blend so I would like to improve that in the future.

- Michael