[CopperTop]

I wonder why the majority of the impacts are in upper areas?

[MtnClimber]

I wonder why the majority of the impacts are in upper areas?

It is likely that the poles are colder and impacts last longer. This is ice over a water layer. There are water geysers so the middle latitude surface may get covered or get melted into the interior to erase impact craters.

[Telepathic Intruder]

Cratered areas usually indicate the least amount of geologic activity, and therefore the oldest. In this case probably the least amount of subsurface ocean.