halo 5 placement matches

So im making some calculations here based on players K/D/A, wins and losses for the first 10 placement matches in the march season and things are not adding up.

a player who has won all 10 games for their placement matches in arena with a k.d.a of 2.9, at the end of the placement gets put into platinum 3

another player who has lost 10 games in their placement matches in arena and a minus 10 k.d.a gets put into diamond 3

is their anything else that adds on to their placement matches? Do previous season rankings attribute to the placement rankings?

Can someone clarify this.

Previous season and the rank of the people you fight will also affect your placement.