Those devices cost a lot to place and duplicate, and when you need one enemy type to spawn 60 times you have to place the device 3 times and do some funky verse stuff to make it work.
Why not allow us to set the max spawn limit of an NPC device to 90 straight away? This will be cleaner and better for performance rather than having 5 devices handle 90 enemies you can have only 1 do that.