A filtration constant can apply to poorly-fitted masks, too. They just have a smaller constant.
The filtration constant for a well-sealed N95 can be 99.99%. The filtration constant for a thin cotton "face covering" can be 20%.
The point isn't that the model doesn't apply to poor masks -- it's that they have poor constants. We will do much better to include them in the model, and then mathematically predict how important it is to improve your filtration constant, than to say "those masks don't apply" and throw up our hands at quantifying the improvement that could be gained by better masks.
The filtration constant for a well-sealed N95 can be 99.99%. The filtration constant for a thin cotton "face covering" can be 20%.
The point isn't that the model doesn't apply to poor masks -- it's that they have poor constants. We will do much better to include them in the model, and then mathematically predict how important it is to improve your filtration constant, than to say "those masks don't apply" and throw up our hands at quantifying the improvement that could be gained by better masks.