Gap between breech block and frame - why

[gunsrfun1]

Hello again - After disassembling and reassembling my Luger (with no parts left over, hooray), I noticed that there is a gap between the breechblock and the frame, even when the gun is in the fired position. (i.e., not cocked). At first I was a little alarmed, but since there's only one way these go back together, I knew I hadn't done anything wrong. Plus, I looked at some other guns on this site, and this appears to be normal. I'm just curious if there is some type of engineering reason for it, since I would not think German engineering would allow such a visual faux pas without reason. I've attached a photo I cribbed from another post (apologies in advance) to illustrate what I'm asking about. thanks