There is a trick with the 9/16" tubular that takes care of the tails and "supposedly" decreases the slippage.
Tie a single water knot and move it away from the bitter end.
Then, open up one of the tubular webbing and sleeve the other end into the open hole.
Be sure you have plenty of "tail" both inside and out, before you work the waterknot back over the sleeved portion.
Check by feel to insure there is extra webbing inside, as well as visually inspecting the outside tail.
I have climbed on this setup for several years without any noticable slippage.