WoodyZ,
I stripped away about 25GB and then converted the file structure to the 2GB blocks. That worked and it did consume about 100% of additional space in the conversion process. Then I added 9GB to the file structure and saw no temporary reduction in overall disk space. (In fact there was no reduction at all, apparently because that new space currently has nothing in it.)
Thanks for the quick and correct diagnosis of my problem.
Cheers,
h__sqd