Sanctuary of Thought
10% less Mana Reservation of Skills
50% less Mana Cost of Skills
1% increased Area of Effect per 50 Unreserved Maximum Mana, up to 100% 
Sanctuary of Thought is a notable Ascendancy passive skill for the Hierophant that grants less mana cost to skills and mana reservation, and additional maximum energy shield equal to a percentage of the user's maximum mana. It also grants increased area of effect based on the amount of your maximum mana.
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 * ( 0.20 ) * (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.