Izzy,

You have hit the salient points and would only add that the main reason a filtration mask works when the virus size is smaller than the pore size of a filter is due to the mode of transportation of many airborne viruses, which is by being attached to dust particles. This attachment is not by any actual action of the virus, but is due to electrostatic charges. The N95/N99 mask works because it is filtering out the dust particles with the virus attached.

Have worked in an infectious disease laboratory for more than 35 years, I can tell you that correct and effective use of any mask requires thought and some training, if it is to be anything more than just window dressing.

Pete