I have tried B_Truck_01_transport_F with all available PiP Graphics settings from 'Low' to 'Ultra' and the PiP mirrors didn't work on any of them. The environment/reflection map shader would always display on the mirrors, regardless of which PiP settings were applied.
The PiP mirrors display for all PIP Graphics settings on B_Truck_01_covered_F unless PiP is set to 'Disabled' - in which case they use the environment/reflection map shader that permanently appears on B_Truck_01_transport_F's mirrors.
The attached image was taken with PiP setting set to 'Standard' in both trucks.