I can confirm what Battalia is saying. BUT... there is one more thing...
If you have a MASSIVE loose streak, I'm talking 10 games or so, it will actually try to match you with people of lower leagues. Since I currently don't want to climb out of diamond league ( even if I easily could) because I don't want to face lvl 13 units ( I don't even have a single lvl 11 unit yet! ) and because I HATE the master league maps, I sometimes let myself drop from diamond 1 to diamond 3, only to climb up to diamond 1 again. During this time, I can face diamond 3 opponents when I'm diamond 1, and if I let my loosestreak grow even bigger, I can get matched even with plat enemies. My record was to fight platinum 3 as diamond 3. But as soon as you win just 1 match, you will instantly face only enemies of similar rank as you.
So basically, the matchmaking works just as intended. If you have a loose streak, the game actually helps you. But if you have a massive winstreak (which I also had), nothing changes, so you will NOT face higher ranked opponents.
Once got matched with bikerush himself (rank 1 player) while I was in diamond, no idea how this happened... I guess the matchmaking didn't find a master/tib player at the time he queued up and he was in queue for a long time, so it randomly chose me. I often see that diamonds get matched against tib players. This sounds bad for the diamonds, but they get a challenge match in literally every match so it doesn't affect them at all. However, it hurts the tib players, since they only get 8 medals per win. And if they loose ( for whatever reason lol ) they loose quite a bit, I've seen someone loose 40 at once, ouch. In addition to that, tib players do not enjoy playing against diamonds, since it's most of the time no challenge. Alicia Destiny is tired of getting those +8's xD