No, the response distance setting has no effect on mission spawn. Only on sending units to missions. Mission spawn radius is coded in and can't be changed. Only time its changed is when you trigger the anti-bot system, and spawn radius is increased to punish you. Otherwise, the spawn radius remains the same.
The mission spawning at max radius is triggered by building to many stations in a close proximity to each other.
The game settings actually has a warning for this you can check it by clicking on a dispatch centre then click on the settings tab, what your looking for would be the last line
Do not show warning message when buildings are built too close together
Unless you have turned that off you would know if this was the reason
So, I switched locations in game from Durham to NYC by moving my main station, but I’m still getting Durham calls. How can I fix this?
If you are moving stations from an area and you will have no stations left at the original location you are best to pause mission generation and complete all missions, then move your stations before you resume mission generation
You can pause mission generation in the mission speed tab