I'm trying to use the Indent tool to make a cavity on a plastic enclosure that a separate part will 'nest' into and be screwed on.  (Through holes have been removed from both the target body and the tool when trying to perform the indent).

When using this shape as the tool body region, everything works as intended.  (The plastic is formed around the elliptical face).

However, once I round off the end face to make it smoother without sharp corners, as per pic below, it fails to perform the indent.  It says to try reducing the thickness but this does not solve the problem.

Any insight as to why?  Or ways to make this work as intended?

Thanks,

Tyler