Alright! I can mostly explain how this works:
It depends on the ranks of the players above and below you. For example, if you were a Novice and got fourth place, but the players that beat you were all also Novices and the players that lost before you were both Grandmasters or Masters, you could gain rank even though you got fourth. The game individually calculates a loss/win against each player: If you placed fourth in that example, it would count the same as two wins against a GM/M and three losses against a Novice.
3rd place can not lose points if they beat three players of higher rank, and lost to players of higher or equal rank as well.
No! I'm just someone who tries to help out :)