Ok then i select the poly plane .. and the little cube and Click on the Icon in Red !? don't know how the function call ...

After i set this function to the poly plane and little cube, I add a gravity field to the big gube ... see in top view for the center .. place it up the little cube and press start to start the frame line .. and you will see it is balanced ... move it right .. press again play .. and you will see it will fall on right

P.S if this is the effect you are looking for ... ( Just a simple sceane you can use it for some complex )