Thanks for your replies... I have about 760 users.
If all users with same points get same rank, then I would have users n° 443 - 760 with same points I guess. Starting score is 10 points, bonus for registration.
Edit: I checked, I have 330 users with score 10 (they have no activity, only registered an account). About 760 - 330 = about 430... mhhh strange, then comes many users with 15 points.
All right, I checked users with 15 points as well, all have the same rank.