The real M9/92fs has a 'gap' per se but it's like 1/10th this size and isn't visible when looking down the sights. I got out my 92fs and checked, if you look at an awkward angle and shine a light down the back you can BARELY see a hint of something brass-y.

Using the somewhat-jank (but faithfully modeled) World of Guns game you can see just how tiny the gap actually is.

I tried to get a sight picture but the camera didn't cooperate.