For InFO packages, the contact area is the package body area. This is because the periphery of the package body is filled with a mold material that is planar to the die. This measurement is specified in the top view perspective of the mechanical drawings. The height is derived from the A parameter.
Figure 1. Example Top View of InFO Device
Figure 2. Example Diagram Denoting the A Parameter used for Clearance and Attachment Considerations