Maybe someone can help me with shadow casting on vertical planes. 
If I put a character in front of a plane which is running a video, and I am try to insert my character in the video scene as realistically as possible,. I would of course like the shadows to function as if I was working against a floor plane. I've spent hours with the spot- and directional casters and put shadow catchers in all sorts of positions and angles but when my character moves the shadows just dont follow in the desired manner. 

I get sufficient results as long as my character is standing still - but not when movement is involved.
Since characters can't easily be scaled, I move them on the both the X, Y and Z  axes to get them deeper into the video scene and that's when the difficulties occur. Can anyone help me.