That’s correct. At fusing
That’s correct. At fusing temperatures, air expands considerably resulting in a very thin atmosphere in the kiln. The lack of air means there isn’t anything to carry a lot of heat through the hole. The glass, on the other hand, is heated by radiant heat (line of site from the coils) so the absence of a lot of air isn’t an issue.
If you want to plug the hole, some scrap fiber blanket or paper will do the trick.
Helios Kiln Glass Studio