THM Astral Fire/Umbral Ice stacking

[Foullacy]

I'm pretty sure multiple stacks of Fire does NOT increase MP cost past the first stack. I can only test two stacks, but right now with one stack my Fire costs 90 and with two stacks my Fire costs 90.

Every stack of Astral Fire increases the mana cost of your Fire spells and decreases the mana cost of your Ice spells. At three stacks of Umbral Ice your fire spells have a drastically reduced cast time and vice versa for Astral Fire.