We're all victims of our success. Here is the link where matchmaking is explained in greater detail http://forum.warthunder.com/index.php?/topic/87904-matchmaking-in-137/?p=1607141#entry1607141 That thread deserves Phaedo's screenshot and an explanation.
Probably if their battle ranking places them around the same level as you. I Kinda like it better this way as once you break into a new tier with a single stock plane you don't get instantly butt-fucked by the more potent planes in that tier. In theory anyway. The new system has a ways to go.
Wow that thread is just a giant flame war. All it is is people bitching "why are you mixing tiers" it take 5 min to get a game WITH mixing tiers imagine if you were forced to only fly your tier!! There wouldn't be any games.