From what you shared above, split-level 1 is correct. With the share name being 'movies' and the next levels being 'movie_name' and 'movie files', this will ensure that the movie files stay on the same disk as the movie name.
A couple of questions for you:
1. How big is each movie directory?
2. During the copy process, when did you decide it was doing the wrong thing? (i.e., can you quantify "well beyond 50%"?)
If your first disk was filled to 1.449TB, it would have copied the next file before switching to the next disk. In other words, the high-water mark (in this case 1.5TB) doesn't trigger until it adds a file that goes above it. That next movie directory file could have been a large one (e.g. 20GB).
If you don't think this is what happened, please let me know and we can look into this further.
On your TV show hierarchy, split-level 2 is correct.
Thanks,
TomH