An RDU fluid injector includes a fluid inlet and a fluid outlet; a fluid path; an actuator unit including a pole piece, a movable armature and a coil; a valve assembly including a valve seat and a seal member connected to the armature and engageable with the valve seat; and a volume reduction member upstream of the actuator unit. The volume reduction member includes a throughbore partly defining the fluid path. The actuator unit, the valve assembly and the volume reduction member are disposed in one or more body portions of the injector, wherein each of the actuator unit, the valve assembly, the volume reduction member and the one or more body portions includes one or more components of the fluid injector. A ratio of a volume of the fluid path to a volume of the components of the fluid injector is between 0.08 and 0.30.