Lets say your at 1800.
You play 15 games, each time you win 0,3+ rating
So thats a 15 winstreak
Then you get a game where you win/lose 6+
You get some completly useless teamates on your team and you lose
You win 15 games in a day, and lose one
OP stop queuing with 1600 friends and you will receive more than 0.3 MMR per match