I found Riot's exact algorithm for role selection in ranked games!
Game 1) Que dodges until you are auto filled.
Game 2) Protection because you recently filled.
Game 3) Protection because you recently filled.
Repeat.
Game 1) Que dodges until you are auto filled.
Game 2) Protection because you recently filled.
Game 3) Protection because you recently filled.
Repeat.
Pretty sure it's actually
Game 1) Que dodges until you are auto filled. Game 2) Que dodges and your auto fill is used up and you are autofilled again Repeat