Oh snap, forgot about Null-Reflect. I remember wondering what the point of that was when I played it a few years ago. Now I know...

Say, when you cast Fira on your reflected characters, does the reflected Fira spread around the enemies, or is it only to one enemy?
It will spread around but the damage dealt can be kinda random
Sometimes it will leave one enemy completely unscathed and other times it will spread the damage evenly
I actually had to take off auto-reflect when I fought
because I thought he'd do a lot of damage (though he didn't, of course it helps being level 60 so early in the game)
But I still ended up using the reflect trick by using carbuncle
Vivi was in trance and I had Eiko summon carbuncle then I had Vivi double cast blizzara on the party
died after the second hit, each hit doing about 8,000 points of damage
Of course I could have just used
Spoiler life since soul cage is undead
but that wouldn't be any fun now would it?
Another nifty trick that I learned a while ago was to use a tent on the enemy. It will cause multiple status effects (ie blind, silence, and I believe poison) to the enemy when you use it on them.
When I fought
I used a tent on him and I had distract equipped so he only hit me once during the battle (doing about 400 points of damage when Zidane had about 4,200)