Tier IV Medium and Heavy tanks should only see Tier 6 enemies at highest unless platooned with higher tier allies. As Sumeragi above mentions however, Tier IV light tanks and above are considered scouts, and thus valued higher on the matchmaker, resulting in them seeing even Tier X tanks. One the one hand, if you can keep yourself alive long enough to scout for the Heavies, you can earn significant amounts of exp and cash without firing a single shot. On the other hand, it's surviving that's the problem