🛌playersSleepingPercentage/countUnderground

"Hey can you sleep?" "No I'm in a cave."

Granular Gamerules adds a setting to remove underground players from the sleeping requirement. This means any players mining won't stop surface players from passing the time until day.

The cutoff for a player being 'below the surface' is 10 blocks below the sea level, or Y = 53. Players that are below the surface can still sleep and count towards the percentage.