That is because loading the disc causes an increase in Nr (flare effect) due to the change in direction of the relative airflow increasing the AoA - blade flaps up, c of g moves inwards (towards the hub) and conservation of angular momentum increases the Nr. As torque required reduces as rotational speed increases, the indicated Tq will reduce. Conversely unloading the head will have the opposite effect. Try it in autorotation with the throttle wound off - we all know if you flare in auto the Nr goes up but try following it with a push forward and watch the Nr decay.