Good eyes! ;-)
That's intentionally. The number of connections of each nexus is limited. And not all nexi are discovered at the same time. When the connection is established at high costs the Imperial auditors will be very nasty if it is changed without good reason.
If more connections are discovered this phenomenon may repeat several times.
The aether ships must stay horizontally within a few hundred meters of the aether line. Actually this ration is better for vertical direction as it is improved by the interference of aetheric and gravitational forces, so that ships can actually rise to two miles above the line.