Selecting exposed faces

All, I have two plates of material A and material B. Plate 1is larger (longer and wider) than plate 2.  Plate2 ispositioned on top of plate 1 such that only a portion of plate1 isvisible.  I need to apply a load/restraint (heatfluxincident) to the exposed area of plate 1.  Currently whenIselect that area, the whole face is selected which is not atruemodel of the real world.  The flux incident will only hittheexposed faces and the covered area will be heated byconduction. I have not attached the model, but I have attacheda ppt fileillustrating what I am trying to do.

thank you,
KevinSolidworksSimulation