This is available on the wiki, but quite frankly can’t be publicized enough. The misconceptions about the matchmaker (MM) are legion. Players new and old should reference this chart often, and familiarize themselves with how MM picks teams.
To give an example of one of the most common misconceptions I’ve referenced before: lets say you and a friend want to platoon. You have a tier 4 medium. He says: great, I have a tier 4 self-propelled gun. Well, Matchmaker uses the tank with the highest battle tiers to place you in a match.
The medium would usually get put in with other tanks in battle tiers 4-6 (yes, these are difference than *tank tiers*) where the worst thing you will see is a tier 6 heavy. But the arty – well, it qualifies for battle tiers 5-8, and since that is higher, MM will use that to place your platoon. Which means now your tier 4 will be facing off against tier 8 tanks like the IS-3, King Tiger, and Type-59. Oops.