The actual plot of air use would look like a stretched or elongated or italicized S instead of rising in a straight (diagonal) line, then horizontally to redline...
Basically, it means that surge is not quite as much of a problem with some of the bigger turbos as the diagrams imply, and that when accelerating, the path will be more toward/in the efficiency island.
If you have a copy of Hugh MacInnes' TURBOCHARGING, you'll know what I am talking about.
Hope this helps...