Well, I found a resolution to my issue.
To recap, after running a volume-to-volume clone from a small partition on a failing HD to a larger partition on an SSD, the filespace available to Windows was the same capacity it had been on the old HD. The Disk Management tool in Windows even showed the full size for the partition, but the C drive only had the original space - and I could not expand the filespace because there was no “unallocated space”.
I booted into the Mac side and used the free version of Paragon Camptune to adjust the partitioning. I figured that, if the partition map was incorrect, even just making a small change (you are allowed up to 2GB in the trial version of Camptune) would correct the partition map and give me the full capacity in Windows.
I ran Camptune - it took about half an hour and ended with an error about “the user has aborted the process” (I hadn’t), but on rebooting into Windows. I did see the full new disk space.
I would love some feedback from Twocanoes as to whether volume-to-volume always uses a block copy, and it is expected to see the same filespace capacity copied across, or if this is an unusual occurrence.