I think you will be a function of engine rpm. Because an F! engine revs to around 18 or 19k then there needs to be some form of reduction gear to match the speed of the wheels to the engine.
It is better done after the gearbox, if it is done before the effective torque the gearbox has to deal with is much greater so everything has to be bigger, stronger and heavier.
Doing it after the CWP again reduces the effective torque seen on the CWP gears and also reduces frictional losses through meshing and lateral thrust. The CW sees the most torque in the system and will also strongest gear. It has straight cut gears so it will have minimal meshing losses to.
Hope this helps, I am sure Scarbs will clarify it further and correct any mistakes I have made
