These are good questions. The issue here is where the viral particles are. If they are in the <0.5um size range, they are like cigarette smoke and go either through or out the edges of most masks, and then hang in the air. IE wearing a mask doesn't reduce the airborne prevalence, primarily they would only work to reduce intake = the video on this tweet shows the effects of various masks on cigarette smoke as an example. (https://twitter.com/Emily_Burns_V/status/1398023020808134656) That twitter thread which is informative, but long, banks on the thesis that something like 87% of the actually infectious viral particles are in the 0.3um size range and hence this demonstration is valid. I'm unable to tell you at this time if this thesis is correct, but if it is, then masks do almost nothing to stop transmission because, by design, they won't catch the right particles.