I think it's the case of you misunderstanding how this feature works. It removes any mesh element that are placed outside of scattered area*. It will not remove anything if your instances consist of single element, like box, or teapot in your examples.
* i'm not exactly sure how the scatter determines when element is considered to be outside of scattered area. It looks that decision is taken not by dimensions of element bounding box, but rather by the placement of its base, which IMHO is very nice feature!