I’m not sure if it is or not. It’s something I’d actually like to understand.

I would imagine that if there’s a significant gap, most air would actually bypass the mask entirely. And “significant” here is still fairly small. I’m thinking you only need a cross section as large as your nostrils for most air to flow around the mask. And as you make the mask less breathable/more resistive, more air will bypass the mask.

But I don’t know how accurate my assumptions are.