Questionable Placement?

Hello fellow summoners and riot team. How does placement work? I'm not looking for specific number, more like just the gist of the formula. Recently I have been playing ranked again in early this month (March). Since the season restarted I was forced to play the placement matches again. My last ranked matches were during January. I was Silver Season 2, stopped play and was Bronze for Season 3, and No lower than Bronze 3 for Season 4. This season I won 8 out of my 10 placement matches. I played 5 different champions and won with 3 unique champions . But I was placed in Bronze 4. I looked up how placements are made and it seem like it has to do with personal performance, win ratios, and previous standings. I checked my honors and they seem fine. I'm rarely upset during games anyway. My standing has never been Bronze 4 with 0 points. I am extremely frustrated on how this happened. Does it have to do with the fact that I played support in 6 out of the 10 games and did not have a good K/D? Or is it something else. I am confused and upset that I can't even play with my friends now because our standings are too far apart. I don't much time to put into league, if I did I wouldn't mind climbing up the ladder but this is just ridiculous. Any advice?