Most mobiles start with small and light pieces and progress to larger and heavier pieces to counterbalance. The length of the wire or armature also can control the leverage. This one goes from the small to larger then back to the small without adding lots of length to the armatures. Most people would not notice but when it is noticed you see that the pieces are made from different materials with different thicknesses and different specific gravity. That is what I was playing with.
Small to Big to Small Mobile