The proportioning valve seems to have small front outlet threads versus the rear. So perhaps it is meant for smaller lines up front.
Look a little closer- - - - -the metal lines are the same diameter on both ports. The fitting threads are different sizes as a method of "idiot-proofing" the installation so the front and rear lines can't be swapped by a ham-handed wrench jockey. Don't believe things like that can happen? There was a particular power steering gear used on some Mercedes models with the pressure and return lines with the same thread. If the high pressure hose got installed on the upper port, the pump would blow out the seals and empty the reservoir up the steering column and into the interior of the car. Hydraulic fluid IS NOT an appropriate treatment for custom leather upholstery!
Jerry
