Regarding the hardware, we're assuming that the module on the side of the diff is calling all the shots regarding how much clutch is in at any given moment. Given that that decision is made with reference to steering angle, throttle position, gear selection, relative wheel speeds, brakes, and perhaps even air temperature, perhaps the choice of 'how much' is handled elsewhere, and the diff mounted module just looks after the fairly complex task of managing the pump and clutch to deliver demanded torque transfer.