The function of the spoiler, is as the name suggests. It is to spoil the air flow off the back of the body. Without it the air will curve down over the rear to form flow eddies close to and behind the body. This causes a drag on the car and reduces its speed potential.
As this car was designed to be a high speed tourer, body slipperness is more important than down force. The spoiler straightens and accelerates the air flow off the boot, to extend the the eddies far behind the body to reduce the drag.
Downforce is provided by the shape of the underside of the body. The curve of the front under tray is airfoil, to accelerate and reduce the air pressure under the body. This prevents the pressure rising under the body to cause lift, it actually reduces it to pull the car down.
Anyway thats the way I read it.
Harvey.
