I’ve wondered this myself which is why I like throwing in a few shorter tracks, but I havn’t noticed much difference in sales between the prices. My portfolio is relatively small though so it’s a hard one to judge! I guess it depends on the style of music and who it caters to, corporate tracks would probably sell just as easily at $19 because the difference in price would be small for most business’. But tracks designed for smaller industries and independent media artists might sell better at a lower cost.