I'll chime in about the grading system as well.
It's retarded. It only rewards speed, which makes for some funny situations. In one map, there's a massive maze of buildings and enemy soldier with the flag guarded by a large number of enemies. If the game were properly structured, it would have taken me a while to defeat it with an A. I would have had to position my troops properly, use CP wisely, consider class mix and auxilary weaponry. I suspect it might have taken me 6-8 turns.
Since it only considered speed, I just took the Shamrock, rammed straight ahead, flammed the "base" to death, and then sent a scout in with Def+ and Awaken Potential and tada~ victory in 1-2 turns.
I hope they fix this for future iterations.
As for Amirox, just do what I did, and play while disregarding your rank. Use different strategies, kill everyone, or not, speed through it, or not, but just enjoy it.