If I understand what you're saying it's possible that the hoop is slightly oversized, or the shell is slightly undersized. The Ludwig shells (and likely hoops too) have varied in diameter slightly over time.

For instance, I noticed that a late 70s LM402 shell was slightly larger in diameter than than a 2016 model LM402.

Lug gaskets are now used to make up the difference in size, in my opinion.

I'd check it on a flat table/surface with a light inside to check for uniformity/abnormalities.

The space you're describing might just be where the snare bed crimps are. You can also check the batter side for uniformity, as well (it should be flat, no light leaks like the snare side where the snare bed crimps are).

I'd check for shell roundness (measure across the shell in an X and + pattern, and the number should be uniform between the measurements).

Do the rods go straight up even with the shell or is there ,...i'm gonna say it,.....no,....got a pic ?