I upgraded the OS, then rebooted, then did my test.
My test report indicates exactly what I did in the commented lines ("#…").
"Right click > Delete" instantly deleted the file (ok for my personal taste, but moving to trash would be fine for majority I guess) and warns about it correctly (only the first time I did not notice it, but it surely happened).
Drag a file and drop it to the trash did copy, not move.
And thanks for explaining that filesystem-compression played a role in the test!
Explained why it fitted on the NAND, and also the delay (=data analysis), which felt too short for a complete copy operation, but too long for a mere move operation. So a trashing operation still crosses filesystems instead of putting it into a trash per filesystem. I know that i.e. Mac OS X does so. It keeps a Trash per Volume (=Mac term for disk partition). Therefore trashing a file is instant, just a filesystem operation, no data copied, and trashed files from different connected Volumes show as "one trash for the whole system" which in fact is just a display aggregation of all Trash-es from all Volumes.
Would try /dev/random for another test.
Or I can spare myself the tests, and explain what should happen in which scenario by design.
Would appreciate this!!! Thanks, porg