What I see on my accounts;
-We are grouped by level, only 1 break at level 100, so you're in a group with 1-100 or 101-200.
-The moment you first log in the leaderboard makes a difference in what kind of group you get. If I start last day with my 2nd account, I'm in a very lazy group and can feed myself without any troubles to 1st or 2nd to get the grand prizedragon, but it also means I don't get the final individual prizedragon...