I have been fighting DAWG's character Magnus this morning, and notice something interesting about Round One of melee. In Round One, I still have two minions remaining, while he has four minions plus a familiar.
Here is what my fireball looks like firing at him:
Max's Fireball hit Buba , Wilbur , Farmer Joe , Billy Bob , Billy Bob's familiar 
And here is his fireball firing at me:
Billy Bob's familiar's Fireball hit Grover , Max , Wilbur , Farmer Joe , Billy Bob 
Notice the maximum number of minions/familiars affected is 5. My minion Grover takes no FB backlash in that round when I fire, and only 3 of 4 Magnus minions take backlash when he fires.
It looks like the FB targeting ability caps out at 5 targets, even though now with backlash and familiars, that number could/should be greater than 5. Backlash is not that big of a deal, especially in this case where we are both slightly benefitting. But shouldn't the backlash apply to all minions/familiars who are no tthe one delivering the magic? NOTE: since the targeting still allow five targets, no one is ever getting screwed out of that fifth hit as far as delivering damage to the opponent. This phenomenon can and will only affect backlash, as that is the only portion that could ever make the shot go above five targets.
Anyway, thought it was interesting. If this has already been covered, I apologize for wasting people's time...