A contestant can see all of contestant with visibility level less or equal to his level.
Internal algorithms allow to use any integer number for visibility level. But user interface gives you only five levels: Blind (-1), Onsite (0), Virtual (1), Admin (2), God (3).
Then a contestant starts a contest by clicking "Start" button, the visibility level is assigned to "Virtual".
Then you manually add contestants into a contest you can select any level. "Onsite" level is selected by default.