Shell: special situation

This is a special situation where the shell does not work well. Would it be logical to fix this kind of situation?
(if you run an offset this is generated correctly in both parts; similarly, the shell should work because it represents the 3D variation of the 2D offset).
In other words: if the offset works, the shell should work like, a similar principle.

What do you think?
shell not good.3dm (181.8 KB)