The sleeve is not completely closed on the lower side (see photo), but that did not bother me - also have any crumbs or "other debris" so that an easier way to "out".
The snaps hold the sleeve securely closed, but however, in my view, the tab could be something more, so the snaps 1 to 1.5cm close below. So now about 1.5cm air between MacBook and top edge of the bag to stay (see photo). Depending on how you use the front pocket, this is "room" of course needed. With a Velcro you could here the scope to some "cover up", but otherwise I'm very happy with the sleeve and will think I stick with it.
Thanks and best regards
Peter