It depends on the state issuing the IRP plate. I drove a company owned Ford E-350 with an IRP plate on the front and a license plate sized sign on the rear stating IRP Power Unit, plate on front.
The following is from the Michigan Commercial Vehicle Enforcement Quarterly:
Michigan is a participant in the International Registration Plan (IRP) which allows commercial motor vehicles to
operate between states with only one registration plate. As such, Michigan is required to comply with the requirements
of the plan. Officers should remember that not all states require that commercial vehicles display their IRP plates in
accordance with MCL 257.225.
According to the IRP requirements, commercial vehicles are required to display their IRP plates in accordance with law specific to the state in which the plate was issued.
For example, Illinois requires that IRP plates on trucks be displayed on the front of the vehicle as opposed to the rear.
Under the IRP, Michigan is required to honor Illinois law.