Sanctuary of Thought
50% reduced Mana Cost of Skills while on Full Energy Shield
50% reduced Mana Cost of Skills
10% less Mana Reservation of Skills 
Sanctuary of Thought is a notable Ascendancy passive skill for the Hierophant that grants reduced mana cost, less mana reservation, and additional maximum energy shield equal to a percentage of the user's maximum mana. It also grants more reduced mana cost while the user is at full energy shield.
The extra energy shield granted by Sanctuary of Thought behaves like a conversion, and is therefore affected by both modifiers to mana and maximum energy shield. With no "more" modifiers, the total additional energy shield granted is given by
Additional Energy Shield = Base Mana * ( 0.30 ) * (1 + % increased maximum Mana + % increased maximum Energy Shield )
Modifiers like more maximum Energy Shield and more maximum Mana apply multiplicatively as usual.
- Mark_GGG (April 14, 2016). "Hierophant Sanctuary of Thought potentially a bug". Official Path of Exile Forums. Retrieved May 1, 2016.