Does that bother ya? At all or are ya just curious?
It may be that they left that area to allow for some of the heat to escape. Maybe. I only wonder if it bothers ya because if its an aesthetic problem there may be a way to cover it. If its just a curiosity then I will not bother looking for a cover.

I have no faith in human perfectability. I think that human exertion will have no appreciable effect upon humanity. Man is now only more active - not more happy - nor more wise, than he was 6000 years ago. Edgar Allan Poe