Maybe you're "over thinking" the whole thing.
When first assembled there is a slight amount of positive pressure created by screwing the tank together. This is evident by liquid seeping out of the feeder wicks as the tank tightens up. The pressure, in the tank then equalizes. Once inverted, gravity takes over until enough negative pressure, combined with "surface tension", is created to stop feeding until the feeder wicks are low enough in liquid. At that point a small amount of air moves up allowing more liquid to flow down. If this were not the case liquid would leak out when the tank is removed.
A variable that would directly effect this would be the diameter of the center hole in the feeder wick. A larger hole would limit the effects of surface tension of the liquid and allow, true, gravity feed and, probably, over feeding and leaking. That could be overcome by having a dense enough coil wick high enough to effectively stopped the feeder holes.
Maybe I'm over thinking it...