I target feed my zoanthids with a baster once a week. I like to mix it up a bit with different types. It helps alot, I have a tank with zoas I do not target feed along with a tank that I do (which is the high end zoas) and I get thicker and quicker results than that of the non spot fed tank.
So i know the original thread later doesn't want to talk about nutrients but it can't be ignored. I don't know which all of the zoas you have it which way or which don't for you but.... Speaking to the point about the tank you broadcast feed growing better... Even if they don't eat, you still might get better growth due to more nutrients from this extra feeding which could change up your water chemistry quite a bit. There could also be other differences such as flow of lighting etc which could have quite a bit to do with growth.