Ranked Placements

So I've scoured these boards for a straightforward answer about how the ranked placements are judged. I started this game 8 or so months ago and just finished playing my first 10 placement matches and was placed in Silver IV. I won only 4 out of the 10 matches, however I got 2 or 3 S ratings, several A and B ratings and a couple C ratings after the games. From what I read people are saying you are placed based on your Win Lose ratio. I don't find this to be true based on my W/L ratio compared to other articles I've read. Does your in-game performance/rating affect your placement into a league?