My theory on the suction effect is more about the deformability of the chip in relation to the recess depth. I think you can create a small vacuum effect when you press down with slight force on two chips that are more or less well centered on each other. If the body of the chip is more rigid, it won't allow the vacuum to be created.
There are electrostatic effects, too, but I don't know if metallic centers within plastics always do this or not.