Don't know about the climbing gizmos David is referring to, but the notch is clearly necessary to keep the cords positioned one atop the other in the buckle so it will create the friction between the cords needed for it to work. Suspect that if the notches wear down over time, the LL3s will slip.
If the notch had the 'V' discussed, it might be much harder to tighten under tension.
But if the cord is of sufficient diameter to slide but fit fairly tightly in the notch, the taper in the notch should retard slippage under tension, as David mentions. Since the device also depends greatly on the friction between the two cords, it also seems important that the cord not have a slick surface.
Will stick with the LL3s for the pack after all, but test to be sure that the cord is large and rough surfaced enough to hold well. Will start with Triptease, and note that the stuff directly from Kelty appears a little larger in diameter than the stuff from TarpTent. I did not want to use ladderlocks because nylon webbing will stretch, and I need zero stretching for the application. LL3s with Dyneema in the cord seemed by far the lightest way to achieve the desired result.
Daryl, you could always ask someone to take sole custody of your camera on the weekends. Those are nice photos, though. Must be a good camera.