And to 5speed;
When you can sit at a FLOWBENCH, with two heads that "flow" the same cfm... the one you can't hear flowing is the one with better MCS... and that IS MINIMUM CROSS SECTION. Now observe the amount of water it took to get there.
I am not telling anyone Cross Sectional Average is not important... it is.
Nor am I telling anyone Flow Bench results are useless. As you posted, they are a standard. But you tell me why 28"? Why not post their max flow and how much water it took to get it there?
Because the average person has no clue what they're reading, and how the process works. Hell, I don't know very much and I did it for many years.