I maxed my characters main three roles out on the Steppe. It's very easy. At the savepoint before the Subterra, before where the Behemoth King and Wolf are fighting, there walks around a lone Behemoth King. That's the one you need. He is VERY easy to ambush, and you can down him under 20 seconds, gaining a good 4000 CP for a very easy battle. Then simply walk away only a little bit and he'll respawn, and then you can repeat it. Easy, and no danger at all. If, by accident, you don't engage the BK with a pre-emptive strike, simply retry the battle instead of trying to fight it, it's not worth it.