The Mana Reservation Efficiency mastery has been replaced as there is now a much larger amount of Mana Reservation Efficiency for Curse Auras on the passive tree." (The mastery was 30%) :
Gameplay Help and Discussion - Reduced Mana Reserved Jewel not working - Forum - Path of Exile
Gameplay Help and Discussion - Mana Reservation Rounding Question [pics] - Forum - Path of Exile
It Is Now Possible to Achieve 100% Reduced Mana Reserved : r/pathofexile
Blood Magic Support PoE Gem
How to activate all auras with 0% reduced mana reserve : r/pathofexile