After a recent conversation with a longtime friend and Autodesk University Instructor, David Garrigues, I decided to post his interesting insight and content from one of his previous Autodesk University classes, on FG Corridor Surfaces. The illustration below displays how pasting EG and FG to together to create a composite surface does not produce the expected or desired result. These results are evident only upon creation of an entirely enclosed corridor, like in a Subdivision Layout, Pond, enclosed Berm or a moat.
Separate EG and FG surfaces
Desired Composite Paste