something I just knocked out quick that aludes to how poser is working this out.

it's rough and ready so don't be to hard on me - tis a quick test to see what line of modeling would be the way to go.

setup - 4 prop boxes, 1 ground plane.

1 single Quad plane

1 quadded plane

1 tri'd plane (the Quadded Tri'd)

1 X Tri'd plane (as above)

all set to : 10 frames drape. 30 frame anim, both collide - Object vertex against cloth polygon & object polygon against cloth polygon - set to on. all other settings left at default.

each cloth set to collide with it's box and the ground plane.

 

once again, this is a rough and ready test, not definiative results.