Using the Shrinking Radiation Zone plugin, I create a large zone where, outside of it, you get radiation.  When I have a smaller zone inside that zone that has the Radiation setting to 0, you still get radiation.  I've set the smaller zone as parentid before the radiation zone is created AND after... same result.  Still get radiation.
Sucks because I know there's not going to be a fix for this or even an update, as this plugin is not currently maintained, yet it's not labeled that way and no one is allowed to maintain it.