I think 30%, maybe 40%, would be a good stopping for Zael, honestly. Unless you just had nothing else to do with your stamina.
I would be happy with 20%, haha.
But I am getting a groove on with it now, I figured out that small flicks are almost always better than trying to get a "perfect" formation, unless that will provide a BIG payoff. Especially in the final boss fight, getting rid of one spark with a flick probably does more for you than wasting a full time bar trying to take out three or four. But Level 4 is so annoying, I (usually) can't kill the shield monster in one turn and the bird monsters purposely keep away from you.
I thought I would use all my stamina today getting Wisdom Flowers, but my first run gave me EIGHT, so I played the Last Story dungeon at work a few times. I'll get my other sevon Wisdom Flowers (for the final job for Maralme) here at home since it's a lot less time to play that dungeon.