This is not unusual. I bought one from Amazon just like that. I was about to send it back to Amazon for this reason, but when I saw another 28ii from another reseller that was exactly the same, I didn't bother returning it.
EDIT:
I've had another closer look at mine, and it's not entirely flush either. The orientation and scale of the picture (and my need of new glasses, apparently) threw me off a bit. It doesn't look quite as severe on mine, but it is there. I also pulled the cover off to take a look at the compartment and it's all very solid, and appears to seal in that location around the batteries themselves, not so much at the outer cover edge.
In short, yes, it's probably normal, and probably fine. On mine it's only maybe 1/4 the thickness of the cover that doesn't sit flush at that location, but it isn't strictly flush like it is on the bottom 1/2 - 2/3 of the case.
2ND EDIT:
After having looked at it some more I think I've figured out why it's like that. The O-ring is on the cover door, around the outer base of the battery box where it connects to the cover (the surface closest to the outside of the DMM when it's all assembled). The door is shaped as it is to help provide and create a compressive force over the O-ring and battery compartment once the back is screwed on tight. If it were absolutely flush I believe it would be harder for it to seal properly because there would be a large span without any arched structure above to help apply spring-like load.
In short, it appears to be built a bit like a loaded bridge positioned over top of an O-ring seal.
The 28ii is needlessly overbuilt and bulky for benchtop and while good, is noticeably less responsive than the 87V for continuity testing.
How so? I've not used an 87v myself, but my 28II gives me a continuity tone the instant the probes come together or they come into contact with something that allows a complete circuit. There's no lag at all on my unit, so what makes it less responsive?