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%) :
Reservation - Path of Exile Wiki
POE Responsive Forum
How reduced mana reserved work ? : r/pathofexile
Anyone else having issues with Conqueror's Efficiency not changing mana reservation? : r/pathofexile
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Gameplay Help and Discussion - Mana Reservation Rounding Question [pics] - Forum - Path of Exile
reduced mana reserverd caster es amulet : r/pathofexile
How To Reserve Mana for ALL the Auras - 273 - YouTube