If you want to grab anything from the 'parent' change, then you'll need to use something like
in the value type.
Having looked at it more closely, the problem I am having is that it is only displaying Buisness Objects and Collections for the runtime values. No matter where or how far I drill down through these, it does not show any attributes.
When I select any one of these, the field remains in the orange colour that indicates the mandatory field has not been filled in.