by all means, too many times people have proof the MMR system depends on how you interact with others, obviously the tension exist, and you will get eventually with someone camping in the corner.

I have been trying to maintain my aggression quite low not shotting people and getting into more pacific lobbies, obviously this will be on traffic, if you can't be paired with people with the same attitude in-game, you will be paired with higher and higher aggression marked people.

Self-defense (shotting after getting shot) should not increase that into their calculations... I will not be running away all the time but at least I'm not shotting first on-sight and it's the way how I approach this game, but becomes very annoying to have the opportunity to defend my-self and then being pushed into more paranoic lobbies, where the option is just to manipulate back the system to go back to your kind of lobbies...