Gen3 Prius Cargo Space (revisited again)

OK boring topic, but I see another on-line automotive community is struggling with the cargo space quotes (for example 21.46 cu ft for Gen3), and I think I recognize some PriusChat members in that discussion:
CARGO/LUGGAGE VOLUME: When standardized isn't always standardized

Gen2 Prius was quoted at 16.1-cu ft cargo space, which I can approximate from my vehicle. But 21.45 cu ft cargo space for Gen3 seems hard to explain, given Toyota says Gen3 only has +3.0-cu ft more total interior space over Gen2. There must also be a change of cargo space measurement technqiue at play here.

Everything I know on this topic is taken from the Toyota discussion of Gen3 specs on the YouTube video posted below:

Gen2 Total Cargo space = 16.1 cu ft (Toyota brochure)
Gen3 Total Cargo space = 21.45 cu ft (seats up) (from video below 4:15 minute mark)
Gen3 Total Cargo space = 39.60 cu ft (seats down)
Gen3 Under Tonneau Cover = 10.24 cu ft (and this is +0.5 ft3 more than Gen2)
Gen3 Under Floor = 1.98 cu ft (and this is +0.5 ft3 more than Gen2)

OK that's all I have official from Toyota.
Unaccounted for Gen2 vol = 4.8-ft3 (approx space above Tonneau + cubby hole)
Unaccounted for Gen3 vol = 9.2-ft3 where is all this volume? some is above Tonneau cover

Gen3 specs video from Toyota...also qualitatively in the video he says Gen3 just has a little more cargo space.

 

Sounds like you might be on the right track Mike...if true, would it be too harsh to say the new method is a step in the wrong direction?

 

ZH, I got the number from Toyota youtube video 4:15 minute mark

I take it Mike is saying the new technique may involve folding the rear seats down and then somehow defining an invisible line separating the rear cargo area...effectively adding the volume excluded by the seat into the cargo volume.