The bottleneck is the bandwidth/users a single satellite can serve at any given time, as a single satellite serves users below where it is at that point in the sky. So when satellites start orbiting over the ocean or remote/uninhabited locations, they are sitting idle.
I would think that latitude distance is irrelevant and longitude distance is everything.
A ship going across the Atlantic or Pacific Oceans would have the satelites all to themselves. A ship sailing ports in the Caribbean would be in a very congested region.
Airplanes fly at a very high elevation which should allow them to access satellites covering less dense cells.
Why would you think that? There's nothing special about north south directions versus east west directions.
> A ship sailing ports in the Caribbean would be in a very congested region.
Congested by what exactly? Most of the countries in the Caribbean don't have Starlink.