I would guess that if air is escaping from the mask around your nose, it is also entering that way, and so wearing masks of that design is not doing much to hel

I would guess that if air is escaping from the mask around your nose, it is also entering that way, and so wearing masks of that design is not doing much to help either you or others. The vent merely hides the presence of leaks, by redirecting the leaked outflow, but not the leaking inflow. The only effective solution is a mask that fits properly.