When you cast Firey Ember & Icy Evanesence in the same combo, are you getting damage from both Firey & Icy at the same time? IIRC, the tooltip says that the highest level CA (of Firey & Icy) will "override" the lower level one, but that might be related to the damage mitigation you get & not the damage it does.
Yes, I do get damage from all three at the same time. The damage mitigation or resistance is what it refers too by overriding. I thought the same thing, but decided to try it anyway, the damage definitely stacks.