1. Don't post two threads even if you have two questions.
2. Normally duration should be the solution. Even because of the Damage per interval field, which actually refers to the duration. It means how much damage should do over the duration. Maybe you messed up something.
2) Yes, how much damage over a duration, so if I set it to 0.1 it gets damage every 0.1 seconds, but I want to increase the duration so that if the unit walks away from the unit with immolation it still gets burned for ... seconds and not just 1 second.