[unknown]
Hello, as I understand it, the implementation of fibers doesn't really have the concept of pulling one end toward another. The fiber creates an "angle" of compression through each tetrahedra and each tet simply tries to contract according to that angle.
You can test this with a simple, symmetrical object and try to contract it without any attachments. In that test, if you wanted to enforce one end pulling toward another, you could paint the weightmap of the fiber itself to be brighter at the end that you wanted to be the anchor.
In this example that I made below you'll see that the larger end compresses and the thinner end stretches. This is because there's just more tetrahedra contracting at the larger end, but not because the fiber has any inherent directionality. I hope I have that right, hehe.