Ranked Placement Games make no sense!!!

Well I was playing my promos for S5 in the past week and won 6/10, I have some friends who won 2/10 and 4/10 who got placed into Bronze 3 and Bronze 1 respectively. I got placed into Bronze V. I really think that i have improved as a player and riot screwing me over like this in the promos doesn't really make sense to me. Can somebody explain to me why exactly this is?