Thats the way the froden stuff works. When you rig it, you can tie a loop knot and pull it through and your knot will jam against the small tube, that way you dont need junction tubing. You can tie much longer material off the back with a shorter tube.
Nice tie man. Never throw the bigguns that much though. Maybe it's because I don't fish for winters quite as much as summers. And people wonder why those flies are so expensive.....time, expensive materials, and the know how to tie them. Well done.