I think the important facts are that certain frequencies bounce off the ionosphere and others do not. And that 5W (arbitrarily) of power put into the antenna b

I think the important facts are that certain frequencies bounce off the ionosphere and others do not. And that 5W (arbitrarily) of power put into the antenna by an SSB radio will have much more modulation power than 5W put into an AM signal where the carrier is present.