Is there a shadow bias control for built-in shadow options in the light node? (i mean not using vex shadow or shadowmap() funtion)

How should i connect the Vop shadowmatte so that my shadow appears in the alpha channel of the rendered pic?

Whenever i connect the output of the vop shadowmatte to the corresponding output of a vop surface shader, it just gives me the alpha of my objects, not the shadow.

Thanks in advance.

Wesley