Hi Gnz,
in the RFM RC D 2.3 4.2.1 Fully operational Duplex autopilot (that's a normal situation) or with one yaw lane inoperative the best range speed is 130 kt (with one pitch or roll lane unserviceable 130 is the limit, without exceeding VNE) and only there we can find this speed.
About the tangent we can extend the line below the origin in the figure (20 % torque) up to reach 0.
Fafe