I am not an authority but I do not believe that intensity is the issue. The signal must first be detectable, that has to do with signal-to-noise ratio. Can you detect anything? Then it's onto the nature of the signal. If it's pure "noise" it's no signal but if there's some periodicity or regularity, then it's suspicious. The periodicity led to the original detection of neutron star pulsars jokingly being called LGMs for Little Green Men. Of course, the most efficient communication is that which approaches "noise" but the SETI strategy is to find signalling beacons, not to eavesdrop on tight beamed scrambled communications.