Hello,
You can set all text file to one Fences by setting Fences rule for that fences.
- Open up Fences configuration Windows.
- Select "Sorting & Organizing"
- Go to "Type-base rules"
- Tick Documents go to "choose a Fence" : here you can choose which Fences you want it to be send.
- If you wish just send "txt files" click on "Documents". Edit a rule : Documents will open up. You can than edit which file extension you will like to be in that Fences.
- Press "OK" and done.

Note : The rules only work for new icons that come in your desktop area. All icons that are already in your desktop area will not be effected.
Thanks
Basj,
Stardock Community Assistant.