I wonder if they're any similar effect at play worth those who sleep/breathe with their mouth open vs closed.

Would need proper testing but the "arm chair" thinking here is two fold:

1. the nasal passage is specifically intended to help inhaled air warm and be mildly humidified

2. A tendency to sleep with your mouth open is more common in those who are overweight and they've often been observed to be hit worse by Covid

I'm mainly thinking point 1 here, as point 2 is probably just a convenient coincidence, but you never know (until it's tested or at least considered by more of an expert in this field than me the amateur!)