I think Hearing Rings should have a distance in feet equal to Wisdom score. If Wisdom is 10, the hearing ring is 10 feet, roughly 2 1/2 meters. You enter that ring and Stealth check against Passive Perception is required. Then have a second Hearing Ring. Same increment. Enter that ring and Stealth check is required against Passive Perception as well.
Basically, the reasoning is that you have to make 2 Stealth checks to get within melee range of someone. That's not easy. Passive Perception is a static DC, usually like 11 or 12 for NPCs. BUT, if there is a lot of noise in the area, the game should give you advantage on said checks. But, if wearing Heavy Armor or it's very quiet, you should get Disadvantage.
