Hi E. that is what I was getting at in the scene where you had only the ground plane, in that case, you do need to have it visible for the shadow to be seen.  Poser needs an object to display a shadow, your ground plane acts as an object when it is displayed. In the above one, the object that makes the road is visible so the shadow is displayed on it.

Try an invisible ground plan and place say a square from the primitives and place your figure on it.  Your figure will display a shadow on the square but not on invisible ground plane.  Now why would Poser ever give you the option of visible or invisible ground plane?  Here is an example, your ground plane's texture is water, you don't see a shadow cast on water, you see a reflection.  If you see a shadow, its because the water is shallow enough that you see it on the sand or muck below.  Jan

By the way, I like the way you are experiment with a combination of IBL and IDL (I'm with you on this a combination of both if you can put up with the long rendering time for IDL).  See how beautiful your last rendering is?  You did an outstanding job on it.  Two thumbs up