Longer Power Cords Sound better?

In my quest for power cords, i have noticed that a longer cord say 6 or 8 feet tends to have a nicer sound in my system that the same models that are 3 or 4 feet.
Power cords i have found this to be true include Cerious Tech, Cardas, and VH Audio....anyone have an explanation?

AND by nicer sound I mean they tend to have a richer midrange, and a more coherent top to bottom presentation.