Asked the S&W rep about this once (he was there for an NRA event at our local range) and he claimed it does not (whatsoever) affect the function of the handgun and according to him, the handgun was designed that way to let water/debris naturally "sink" its way out of the gun.
Not sure I bought it completely, but I had the same question too, I have a gap on my 9FS as well.
All is fine. as its been said, enjoy your handgun!
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