Mana Leech not working?

edit : nvm, leech resist is just too damn high ... avg 2000 physical hit with 12% leech only leech 3 mana against t15 mobs, very balanced.

Insta Leech on Crit , Inevitable Crits from Ascension as Oracle , 20% Phys Life Leech total -> Nothing with 1966-3247 Main Hand Phys Damage on tooltip.

Mana leech with elemental cold and Oisins Oath support ( mana leech from ele instead phys ) the same.