What is going on with the matchmaking?

I used to play alot of Ranked but am now just playing the game casually but since my account still has about 1500 mmr i obviously get matched with people the same skillgroup, and thats not my concern. Where the problems start is when i try playing casual normals with friends that are alot lower in mmr. I would expect to get enemies that are somewhere between my mmr and my friends but what i get is usually enemies that actually have about 400 mmr higher than i do (?!?) . Meanwhile my team consists of people that are about 1300 mmr, the mmr i would expect everyone to be. How can this make any sense that when im playing with friends that have a lower mmr than me i all of the sudden have to face people that are even higher in mmr than i am??? Cant even enjoy a simple normal game because everytime i have to watch my team and friends struggle against way better opponents, which pretty much takes the fun out of playing in the first place

anybody care to explain?