The message here is, don't bother with munitions that lower your spawn times. If you already have all the existing spawn perks, you will probably be on the 85% cap. And this cap applies to the first spawn, and won't allow a benefit on the second spawn time, even if this time hasn't met the 85% cap.
So my experience here is with the Rapid Deployment Radio as I am only Atomic level. By the time you are high enough to unlock the Emergency Alert System, the spawning benefits will be useless.
If these caps had been displayed clearly somewhere in the game, I could have concentrated my efforts on another munition and not wasted a lot of time on this one.