I've played the skill quite a lot, so here's what I do know:

1) If you kill the monster and it is a not a Lord (or bosses), you should control it if the skills is being cast when it dies, no matter what.
2) > 0% I suppose
3) Everything but Lord o Boss tier monsters.
4) 3 follower tier or 1 specialist type, the strongest kind of normal monsters.
5) As long as you dont overwrite them, logoff or they dont die because of damage.

Hope this helps.
Cheers.

I read on a parasite guide somewhere that seemed reliable that we can have 3 'ranks' worth of controlled monsters. So you could have three rank 1 minions, a single rank 3 minion, or two minions that are a rank 1 and a rank 2. And also yes the strongest enemies like those demons of fury (or whatever they are called, the large ones), or those large mashing-machine robot ones, they can never be controlled afaik even if they spawn as a yellow-named tier enemy instead of an orange-named tier one. I think any enemy type that can be the random area boss at the end of an expedition cannot be controlled, but everything else can.