Thanks, but better spare your brains for a more worthy cause :-)
I've been trying to make sense of it too, but failed so far.
It doesn't seem matter if data has actually changed, and parity calculated, of if Update exits immediately. In the example above, DRU3 was the only one with new files, and it went to standby, while PPU0 stayed active. In other cases there had been no change at all, and all disks were spinning, etc.
On the software side, I have only a small part of what's in your guide : Webmin, VNC, Samba, and FlexRAID.
I don't see any process that could prevent the drives from spinning down... and if there were, wouldn't it also wake them again after I did it manually ?
Come to think of it, I did tinker with NFS exports in Webmin at one point. Maybe I should check that out...