Hi,
in the element context you have various Add * Diagram selections. Once you click one of them the standard dialog creation box pops up (with the respective choice). Now you can select any diagram you like.
Now - what for cluttering the context if the next dialog box gives you the appropriate choice?
Further - the New Diagram icon could be changed so it creates the diagram inside the selected element the same way. And not inside the enclosing package - which is confusing EAUI.
And (more EAUI) if you select another than the pre-selected choices the diagram is placed in the context of the surrounding package - where you can move it manually into the element. Does not make much sense this way, does it?