5s ranked matching

OK so i was just wondering how the ranked matching system in 5's works. For example I don't understand how we play 5 promotional games all against generally silver gold plat players, and then get paired in bronze 3 after going 4-1 out of the fives games. So our team is like what ever well climb.... fast forward 3 games we win the previous 2 convincingly... in the 3rd game we are paired against a plat 3.. 5s ranked team while in bronze .... i dont understand???