The Interaction Engine is currently in a beta state. It works well for the types of objects that you can see in the Interaction Engine example scenes, namely cubes and spheres around 1-2 inches in size. (Smaller and elongated objects in particular are know to be problematic.) When creating game objects of differing shapes, sizes, and physics settings, you may encounter situations where the results are not what you can reasonably expect. We encourage feedback about such situations so that we can continue to improve the Interaction Engine.