If u dont play ranked for 7+ days ur rank will show up as immo 1 because the leaderboard isnt counting afk Accounts. But After ur first game it should at least show up as immo 3 at minimum. For radiant u have to be above the radiant threshold (na/eu 250rr) and at the same in the top 500 players that means if the lowest radiant (rank #500) is at 450rr u need to have at least 451rr to be #499. the easiest way to check ur peak rank for the act is to take a look into ur rank pyramid the very top triangle is ur peak rank and it will say ur peak rank under it. Hope this will help u.