If you get the zoas to be used to food particles they will close and keep it. In nature they do that! People say they close because of reflection of something touching them, but they keep the food. If was reflection they wouldn't ingest the food.
Target feeding is ok in most cases. You can use invert liquid food, but do not overfeed because of algae problems. I would say if you get a good skimmer and want to feed a lot they will like it.
Some zoas come from "nutrient rich waters" while some others come from relatively "clean water". That's why people have problems with some species and others do wonderful in their system. It's relative. After a while you'll see what works best for your system and the organisms you have in it.
Feeding your fishes is a good way to keep zoas happy in this regard.
Grandis.