nope, mine is flush like the pic. i couldn't fit anything in there. not paper, advertisement slick from the mail, nothin
EDIT - i even held a mirror up to see where those puffs where comin' from and it's right out the set screw holes. screws are there.
It's not actually. The large hole in the bottom center of the body has a slight countersink on it that forms a bevel so there's no top corner? The air goes in there. There's a similar bevel on the top edge of the flange just above the threads, you can see it in the photo above were the arrows are? Just above there. Notice you can slip a couple sheets of paper in under that flange?. It the camera above was half an inch or so further down you could see it in the photo above.
The holes are half covered (by design) by the body, they're directly under the screws. You can only see them from the side and under good light and magnification usually. Having a LL cart (much bigger countersink in the ceramic body, the holes are wide open rather than blocked, makes it easier to see.
This is what the inner sleeve looks like:
The threaded hole you can see in the center, to it's left is one of the holes used to secure the heater, below it, before the flange, is the vent. In the LL and EL cores this hole is not covered, in the EO core it's a little over half covered and buried deep in the crack. You can barely see the top edge of the hole in this shot of the assembled core if you look very closely:
Look for it just above the flash line in the metal lighting. It's a dark crescent on end even with the line through the larger hole the setscrew is in. Tiny and very hard to find for sure, the tiny part is part of the job, the hard to find part just a bonus......
OF