Due to the platforms uniqueness condition for relation classes, it is only possible to add exactly ONE relation of the same type between 2 classes in the same direction (as the described behaviour above mentioned).
This means that the intended behaviour can only be reached by adding new connection objects on the actual object. Through the “is-inside” auto-relation, it is also feasible to identify which object is on-top of each other. For this purpose the container object has to be derived from the "__D_aggregation__" abstract meta-class.