When i received an attack with fireballs, my bonus for the level units don't working, and the real damage is the double registered by the game. Example
1 fireball of 16k kill 30k of my units, but the battle report reflects just 17k of losses
Ive never seen a fireball attack do more than 1:1 ratio of damage, not saying it didn't happen as you described. Personally, I've used quite a bit, and always end up with a 1:1 ratio.