Three references:

First is a definition of position di rigore in italiano:

http://www.aliseocommunication.it/index.php/component/glossa...

Collocazione di una pagina pubblicitaria in una particolare sezione della testata, a richiesta dell'utente o dell'agenzia. Le pagine di rigore sono: le pagine di copertina, la doppia pagina, le pagine di destra etc.

Second is a Rolling Stone page on advertising rates that refers to cover positions and special units. This is the translation that I would use:

http://www.rollingstone.com/services/pages/advertising-terms...

All orders for cover positions and special units (e.g., gatefolds, inserts, scent strips, center spread) are non-cancellable and close 30 days prior to the advertising close date for regular issues, and 60 days prior to the advertising close date for awards issues and special-themed issues

Third is an Italian translation of special positions by an Italian magazine (so I'm thinking less likely, but not so different in the end). To see "posizioni di rigore" change the language of the page.

http://pubblicitaonline.edidomus.it/stampa/index_listino.cfm...