From what i looked at, there is pretty much zero effort to pull in someone else.
There better not be. I'd be pretty pissed off if I queued up by myself in a Normal game the matchmaking system made me waste my time in a sub 30 game to 'balance' things out.
I imagine that not many Challenger players enjoy low level games, so I doubt they queue up with their pre-30 friends that often. When it does happen, it sounds like the system does the best it can to compensate.
From what I know about the matchmaking system, this is what I think is happening:
Pacov shows up in LAN and makes a new account. He starts stomping beginner players from Costa Rica. Great win percentage, huge KDAs, good fun.
Oh no! The smurf detector notices this. He's now registered as a smurf. The matchmaker don't know if he's Gold V or Challenger. Pre-30 games are a total crapshoot so it's really hard to tell. So when a level 30 Challenger enters a Pre-30 game, the system says "What the fuck? Well... This Pacov guy is pretty good. He might be Challenger too for all I know. Let's see what happens."
If you were curious, hopefully that clears up a little of the mystery.
If you were complaining, keep in mind that the actual beginners who are learning the game don't want to play with you. Riot doesn't want you to play with them either, so if you're ending up in games full of NA smurfs then everything is working as intended.