Tom, in my AR training we never connect directly harness-to-harness. We always connect the victim and the rescuer to the rappel device independently. You still have control of the descent and can position the victim for best rescue, but you don't have any of the complications of loading a harness in ways it was not designed to have. I don't necessarily mean loading in ways that could cause failure, but in ways that pull it out of shape, giving trouble to the wearer in terms of mobility and comfort. No reason that I can see to do it differently.