Confused on how placements work.

Just to clarify, I'm not whining about where I was placed, just confused about it.

So, I did my placements and finished with 6 wins and 4 loses. During last season I finished in Silver 4. My rating I received after the games were as followed. 1 S 1 S- 1 A+ 3 A's 1 A- 1 B+ 2 C+

I had made sure to keep wards on the map, and replace my pink wards when they were destroyed. I ended up not dying in 5 of the games I had played.

Here are my stats. http://imgur.com/xIIbKfB

Just wondering why I was placed so low.