to clarify: the tube is intact up near the top, right? it's just the "back" end of the tube that's damaged, right?
I've kept exactly 1 FD for the past 9 months, so take everything here as a newbie opinion.
Feather dusters like nice laminar slow flow, as far as I know. If the crown seems like its blowing around, the the flow is either too trbulent, too forceful, or both.
FD crowns sift particles. the large particles become part of the tube itself. This process is as I understand it, fully automatic, so the tube just continues to grow in time. and the back end falls off/apart.
soft tube FD's naturally live in soft sediment. You might try burying it partially in the sandbed, but that never worked for me. What has worked for the past 8 months or so is I drilled through some LR, and eased the back end into the hole. Over time the animal has continued to extend the tube forwards, I expect one day to see the tibe tipped out of the hole, at which time I'll probalby try putting him in a PVC pipe filled with sand.