Please note that I'm referring to the Mover script - it's moving files already on Unraid from the cache pool/drive to the Array-protected disks, so it should already have the files sizes known.
If I'm setting a share Minimum Free restriction to 4GB, the movie file is 4.5GB and the subtitles file is 40kb, with a split level that restricts the subtitles & movie files to be on the same disk, and the mover moves the subtitles file to a disk with 4.1GB free, the movie file will be stuck on the cache drive.
If the mover script will move the files ordered from largest to smallest, the movie file will move first to a disk with enough free space, and the subtitles file will be moved to the same disk...