If you have multiple classes with the same name from different classloaders and want to differentiate between those classes, you have to navigate to a specific instance, go to the data view of the heap walker and continue with the class selection as described there.
No specific view settings apply to the classes view.
A new object set will be created that contains only the instances of the selected classes or packages. After your selection, the view helper dialog will assist you in choosing the appropriate view for the new object set.