So...Placements

I know, I know, it's pre-season and whatever, but I am very, very confused as to how they work.

I played my 10 just to get them done and over with and I am honestly surprised by the results.

I won only 4 of them because 3 of them had an afk on MY team, 1 was full of heavy feeders, and there were 2 I definitely deserved to lose. To be honest, one of my four victories I was carried.

And despite having lost 6 of my placement matches, I'm placed in silver 5. It's where I ended season 6. I am not complaining. I just expected to be in bronze again after what seemed like a bad performance.

What, exactly, is taken into consideration for placements? Because winning and losing does not seem to have much of an effect.