If you look at the photo of Charlie Craven's sparkle dun below, the zelon fibers naturally spread out when tied in. I believe they initially they fall on the water spread out and support the fly.
http://www.charliesflyboxinc.com/uploads/DSC05485.JPG
Although I use the image above as an example, I think if you search google images for sparkle dun, the tail is composed of spread out zelon.
http://www.google.com/search?client=...PObj0QHgxfWUAg