This isn't a spatial metaphor any more than "upperclassmen" and "underclassmen" are for high schools or "left" and "right" are for politics. We call it the "upper" chamber because it's supposed to be the higher status, more "dignified" chamber.

Words have histories of course, and probably at one point this was a spatial metaphor - maybe some bicameral legislature literally did have one of their higher status body on a different floor than their lower status body. But the words upper and lower when applied to the legislative branch have evolved since then.

The Senate alone has the power to confirm every judge in the entire judicial branch. The House has absolutely no say in any of that.

The Senate is who convicts impeached officials. They approve judges and cabinet appointments.