Seeding the artist editor with new URL relationships leads to a new field being displayed under "External Links" but the text is empty, e.g.
If the link type parameter is removed then the relationship type must be selected, but the Twitter icon is displayed next to the input field and the available types are restricted to "social networking" only, which indicates the URL must be being parsed correctly:
Also, the index number within the parameter (e.g. edit.artist.url.N.text) name appears to have no bearing on where the new link is added in the UI. If only a URL parameter is included then the field appears as #1 in the list regardless of index, e.g.:
However if a link_type_id parameter is included then the new field appears as #2 in the list regardless of index, e.g.: