Riot Please Explain (Ranked Placement Inquiry)

I don't know if this is the right place to post this or not (if its not please tell me where I can) but I had just finished my ranked placement matches I won 6 out of the 10 games I played and I finished them all with a decent kda/score and I got placed into Bronze IV, I'm just wondering why so low? season 4 on my placement matches I only won 4 games out of the 10 games I played and I got placed into Silver V? With winning more games in my placements than last year that means I have improved does it not? I expected to get the same results as last year due to winning more games than I did last year? not worse results as if saying I have gotten worse at this game which is how I feel after dropping from Silver to Bronze due to placements that I feel have incorrectly placed me. I'll appreciate any kind of response I get to this I just want to know how this works.