..yes but why would there be a white arc if there were no flaps?
Now, what a good point ... obviously, I opened my mouth prior to making sure that my brain was engaged
Reminds me of an occasion decades ago when Julius Sumner Miller posed a question over coffee to the assembled academic staff at Sydney Uni .. would a cutout in a steel plate get bigger/smaller when the whole was heated ? .. legend has it that Harry Messel, with a throw away answer lacking consideration, opined "smaller" .. from which we should all take the lesson that one should ensure the brain
really is in gear prior to opening one's mouth ...
The references are still useful for the OP so they can stay there.
However, we will all need to wait for someone brighter than I to come up with a better answer, I guess....
DJPil should be able to offer a comment, I'm sure.