You said it's in FWD until slip is detected. That's the part that isn't true. Ford's programming takes into account steering angle and throttle position and will send power to the rear before slip occurs - to prevent slippage.
That's all I was saying.
As for only sending 50% of the power to the rear, Ford has reported in the past that it could send up to 97% of the torque to the rear if necessary, but I can't find any links right now.