What you just said is almost exactly how I have my duncan. I have 2 different types in my tank, my newest looks just like that. Supposed to be a "whisker" coral...IDK if that is truely its name, but it is def different from my other duncan. The one, like yours, has a much larger head to it, fewer tentacles, and the kinda red/green coloration to it. My other, and first, is yellow/green with a smaller head, but many more and longer tentacles.
Either way, I feed them every other day small pieces of mysis shrimp. It is easy to thaw out the cubes in warm water. I toss some mysis infront of my power head for the fish and then handfeed both duncans. If I don't feed the fish prior they will try to steal it out from my duncans...pesky little buggers!