incorrect less mana reservation rounding · Issue #1211 · Openarl/PathOfBuilding · GitHub
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%) :
reduced mana reserverd caster es amulet : r/pathofexile
Development Manifesto - Aura Reservation and Reduced Mana Support Gem Change - Forum - Path of Exile
Gameplay Help and Discussion - Reduced Mana Reserved Jewel not working - Forum - Path of Exile