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Hmm ... I have never though about the masks and just assumed they would cover the nose "automatically" and I would maybe do the same thing.

Which such small masks, people probably believe they are doing something wrong when they are not tight against the skin (like a gas mask or scuba mask) and then puts them over the mouth where they fit tightly.

The mask people probably have experience with are scuba mask or gas masks and they both need to fit tightly.