Shadow Catcher, not fully white so leaving a line where it shouldn't

Here is the setup, I tried increasing the white level of my render layer for both alpha and image in order to eliminate the grey area of my light cone, then I tried multiplying my shadow pass over this, but it’s not working. Help.

As you can see, my viewer shows the result of what I am trying do as white, if you look at my renderlayer you can see the grey light falloff of my light, which I used to create shadows, as can be seen in the composite below, I have this highlighted area which is not uniform over the image. I just want the shadow.

I dont like this behavior too. But i solve this problem by using dilate erode node on planes alpha and than using the alpha over node.

Hope this helps.

Take care.

Thanks so much, will give it a go.

What I ended up doing was resizing my shadow catcher plane, dragging its edges in to fit within just the area I needed.