Currently percent mana bonus does not stack well, because bonus is added instead of multiplied. For example you have Cape of Plentiful Mana and Plenor Battlecrown, but they will ignore mana produced by each other.
Consider a level 8 TB with ice aura, fire mana buff, Vlemish, Plenor, and Cape.
Base mana = 6.88, ice aura = 9, Vlemish = 15, fire mana buff = 50%, Plenoe = 70%, Cape = 400%
With current calculation: 191.456
With multiplying calculation: 393.72
So I wish percent mana bonus was calculated using multiplications instead of additions.