Open the AntiSubNet found in the Terrain\locations folder with S3D.
You'll see they are placed and unless you change that?
They will always be in Game just like Harbor stuff is.
Now to test this? Just change one to say an area you know has no nets.
then run a test mission to see if you get the Rockin Robbins on Latte sound.
Figureing out the distances is another matter for placement.
Lets take the placement for Manila as an example..........
X is 1950.648, Y is 0, Z is -877.4425
So take one of the Nets Placements and change to roughly that area and see what happens.