LozBoz63

This may sound an odd idea, but offer an option to write zeros to all the free space on the volume. i.e. prehaps create a 1MB file full of zeros and then move it across the free space Why? well some storage arrays detect all zero writes and use them to deallocated the space from a thinly provisioned drive, thus you allow the storage array to know there is no longer any data in those blocks

May I suggest a defrag for volume shrink option, It would do a quick defrag but concentrate on ensuring all the files are moved to to front of the volume.