With the WRC cars, they were basically given a free rein, providing the alterations fitted within the dimensional limitations placed on the WRC cars. And because there were no homologation requirements, rearward visibilty was not a concern (as there is NONE out the back of a WRC car).

With this in mind Ford developed a spoiler that created more downforce AND less drag. They also developed the FRONT spoiler so that it had equivalent downforce when going sideways, as the existing car did in a straightline .