Your MMR is only affected by KDA, DMG, CS, how many turrets killed and other stuff **IN THE PLACEMENTS GAMES**. Then After you got you ranked your gonna have a few game (about 10-20) where you stats only matter a small percentage. After these games you have got your "true starting rank". From here your Stats matter ZERO. The only thing thats gonna make you lose/gain more/less LP is by winning or losing. If you lose 10 games in a row you gonna lose 20 Lp and gain 17. Even if you finished all games with a positive KDA. I have tested this theroy on 3 Accounts. And sofar its true.
In the Screenshot every game i won there i got **+16 LP** and on the Losing games i lost **-21 LP**. My KDA was ok and i was trying my hardest NOT TO FEED. Im in Gold 4. And i tested this on my other Gold 4 Account and 1 Silver 2 Account.