Theirs a lot of places I listen to that do what your referring to as a double move up or progressive move up.I believe the spread or even distribution of companies throughout the boro is the priority, not the physical distance of the relocating company.
If they pull every company by distance they would wipe out a whole n/s/e/w side of a boro is my thought.
Eventually, they have to skip over many closer companies because they need to leave some sort of coverage within the span of the area…unless they do a double relocate which seems not feasible. (Ex reLocate ladder 100 to ladder 200. Then relocate ladder 300 to ladder 100)
Just my own assumption.
Which in this case could be a Brooklyn or Queens truck to the Bronx and then the SI Truck to the Brooklyn/Queens house. Cuts down the time the units are on the road to the cover assignments.
Also I don't know, does FDNY "respond" to move-ups? I know several places (especially LA) the have Code R Move ups where the units will respond to the station they're covering if theirs a critical shortage in coverage. Not sure if that's in play in NY or not (with the traffic some day's t would make sense).