Originally Posted by Camron Rust

Players can extend their arms any direction they want...as long as they don't commit a foul with them.

Verticality is only relevant when considering a possible foul call. They can put them over the lane, over their opponent, or just about anywhere short of committing a foul.

Occupying a space also doesn't rely on the position of the arms. If they are not touching part of the court outside the space and their feet are not extended outside the space, they're in the space. There are no requirements on keeping the arms in/over the space.

However, once the arms are out of their space/not vertical, they are at risk for a foul if it hinders their opponents play....such as keeping them from getting to the rebound. But then, that's a hold with or without what you cited.