Well observed there Lucas! The banana is really just a large zingiber-looking plant, isn´t it? Looking good there!
Are mushrooms an option for you, because they might fill a niche on the logs around the circle and under the shade of the bananas. Or how about a groundcover? Sweet potato? Hmmmm
RE: Why have a "banana-circle" when you can have a Zingiberales-circle? ;-)