Does The Chalice of Harmony passive scale with Mana regeneration or Mana itself?

I've noticed that the passive says it restores 2 percent of missing mana instead of *mana regeneration *increased by 1 percent for every 1 percent of missing mana. So does this mean that if you have more mana then the mana regeneration increases, or if you have more mana regeneration then the passive increases your mana regeneration?