As far as I know, if you cannot see the model, you cannot see the cone. I'd argue that heavier armors giving disadvantage is supposed to resemble the obvious pitfalls of sneaking in heavy armor. That being said, if you're strong enough to wear heavy armor, you're strong enough to maneuver in a fine-tuned manner, limiting sound.
If you were to dive into sound, I'd argue that elves should be able to hear up to a mile away given proper noise ambiance. I'd also argue that you'd be able to discern much more from noises, like direction of movement, enemy numbers, and possibly equipment types. My next argument would be that the original dark vision visual should be reinstated in the case where senses are properly calculated, only expanded to characters with stronger senses than others (not exclusive to darkvision). The result would be specific races being MUCH more capable than other races based simply on the fact that humans might as well be deaf and blind when compared to an elf. At what point do you draw the line?
I argue that the current cone system is not without faults, but expanding to the other senses in a more in-depth manner is a waste of effort when you could simply slap "disadvantage" on a heavy armor piece and have it justifiable from multiple angles.
