War Thunder - How does shell penetration work, anyway?

It doesn’t. That’s how. Shot through wood, through chassis metal, through armor plate, through chassis metal, through chassis metal, bounces off radiator, somehow misses the rest of the chassis metal, bounces off wood (?!), through armor, chassis, and then out the other side through the radiator it previously bounced off of. Then my transmission catches fire for no apparent reason. What in the fuck.