The upper cover we also have four holes in side of cover,please as per the attached file picture.
This time engineer make the design for this upper cover is join together with the cabinet,so now can`t change to same the base cover.
Next time can do,becase it design in beginning,so now can`t change now.
If you need the cover with holes ,there are also have four holes for connection is also enough.
Hope you understanding.
Next time can change.