Yes, I know it's not an error message. But it's a sign that you've reached the point of maximum vapor production too, if I'm not mistaken. Your draw creates more vapor up to the point where liquid is not getting to the coil fast enough and vapor can't cool it fast enough. Then the temperature rises. As such, I guess that hovering around the limit of your wick/coil system would lead to optimal vapor production. This without considering the time factor, which you rightly quote