The valve being for air and with small passage in it might be the limiting factor when used in your vacuum system. If it is quite restrictive you might not notice any difference if the valve is in the cab or on at the axle.
Large line to rear and solenoid at the rear should be most responsive. Suppose could have a vacuum reservoir (with check valve) located at the rear between engine and solenoid valve, then the vacuum line size running to the rear is of little concern.
