I understood what you meant about blocking air when the fan isn't being used (turned on). I still say the blades don't block as much air as one might think. I say that as one who rarely turns the fan on but always has the lid open for air to come in on it's own. It's surprising how much air comes in with blades appearing to block a lot of the opening.
I really don't use the fan much.
Just my humble opinion.
Joy A. & Lily
and "Puff", too
No. Ca. Sierra Foothills