I know about the enchanced senses and such but...no one can seriously hear footstops from very long distances could they? That sounds bloody impossible you would have to sense or feel the soundwaves that derives from such a small sound to be able to direct exactly where they are at for you to fire your arrow and then you have to predict which direction they will move to ascertain the direction of your line of fire.
Footsteps echo in a cave, that echo can be used by the Falmer to detect your location... perhaps.
lets see the 5 main senses
sight-unless the poisons are finally wearing off falmer cant see
smell-they have recessed noses and not the hint of a muzzle so they probably cant track via scent
hearing- most possible fluff wise but unlikely based on them in the game.
taste-they don't tongue like snakes
touch-also likely, they could have toph powers
then there is the possibility that their inherently magical mer blood allowed them to develop some kind of magic based sixth sense like a none stop detect life and dead spell.
The size and shape of the nose doesn't really make much difference, so far as I know.
Toph? Either that's a fortunate typo, or intended. It's probably not quite as plausible as other theories, but still a good one. Toph was only able to see with her feet because of her Earth bending abilities.