I'm just thinking this but... As we all know Mist energy is naturally in Cradle's atmosphere originating from the core. By my guess Mist Energy makes up around 2-4% of Cradle's atmosphere, and it takes 22 hours for Mist energy to fully replenish from 0 to 100.
Here's my idea, I am assuming that as you get closer and closer to the core, the air becomes more and more concentrated with mist energy, and thus due to this concentration, the mist energy tank should replenish slightly faster as you go deeper down.
Anther idea to support this, it may be needed to aid players at deeper levels, as mist energy runs out fast and for some players like myself, CE is unavailable or hard to get to.
would it work?
That is a really awesome idea, and it works perfectly with what we know about energy and the clockworks :D