Smart Groups auto playback

Question about how smart groups handles auto-playing the next part in a group. Example:
I play ‘Lord of the rings: Fellowship of the Ring Part 1.’ When this file is done, instead of playing ‘Lord of the rings: Fellowship of the Ring Part 2’, it instead jumps to the next movie all together-- in this case it jumps to ‘Lord of the rings: The Two Towers Part 1’. This is true for all my groups. They auto play to the next movie.
How can i get a ‘Part 1’ and ‘Part 2’ file to play back to back automatically?

The problem is this grouping is also for same movie and different files/audio/resolution/etc. and you wouldn’t expect to play those back to back. Perhaps if it is specifically “Part” it could.

Since there are not too many of these multi-part movies, you might consider merging the two files together as I and many other LotR fans have done. You can use Mkvtoolnix.