Discussion: Why do I suck at Tier X?

I want to get the community’s thoughts about something I’ve noticed with myself and with others recently: the fact that otherwise decent players can be terrible at Tier X.

I’m not a great player by any measure, but I am above average and I’m able to do pretty well in my favorite Tier VIII and IX tanks. I have between blue and purple WN8 ratings in some of my favorites, like the T-44-100, Leo PTA, T-54, Obj. 430, etc.

However, when I play tier X, I’m just average or bad. I struggle to play tanks like the Obj. 140, Leo 1, and Obj. 430U above a painfully average level in tier X battles, even though they’re basically the exact same as my favorites just one or two tiers lower. I struggle to even do my HP worth of damage in many games, especially if on a map not suited to my vehicle. I’ve noticed this trend among friends as well.

I run the same equipment and have 4+ skill crews on all my tier Xs, so I don’t think it’s a matter of setup.

What do you think the reasons for this are? How can I (and other players) get better at playing tier X games?