My point was that measuring the energy of a photon is independent from distance. A given photon's energy will remain the same until it interacts with something.

My point was that measuring the energy of a photon is independent from distance. A given photon's energy will remain the same until it interacts with something. The maximum allowed intensity in the ISM band is a known value, 1W; but the energy of the photon is what you should generally be concerned with.