All premium tanks might have favorable match making. | WG MM patent.

The MM patent goes as follows "…. The battle table may provide an advantage to premium vehicles by limiting the tiers of other vehicles against which a similarly tiered premium vehicle may compete. Battle level difficulty may be adjusted by adjusting the ranges of permissible vehicles in each battle level. "

Aswell as "… players who have just acquired a new higher tier vehicle are encouraged by being placed into battle sessions near the lower boundary of that vehicle's accessibility range, which allows the player feel more comfortable in the game. With time, the balancing system starts putting them into higher levels battle sessions, which creates a challenge of playing with more upgraded opponent vehicles. "

edit:

And "… According to other aspects, each vehicle may be one of a standard vehicle and a premium vehicle, where a first premium vehicle is associated with a lower range of battle levels than a first standard vehicle of a same tier and/or type as the first premium vehicle. "

And ".. In some aspects, assigning may include calculating the permissible range of battle levels as a function of a number of battle sessions previously played using the vehicle. "

This means that the matchmaker favors premium vehicles, and also takes into account other battles you played with that vehicle when putting you into a new battle. When you just unlock a tank you will be put into more favorable matches as well.

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