Each individual's voice is different. Therefore, every vocal artist who performs a song will perform the piece in different tones (too high for some soloists, too low for some some others). For this reason, while the song is being performed, the musicians perform the work in a tone appropriate to the voice of the vocal artist.
While it is possible to perform the work in different tones by changing the tuning by applying different methods in many instruments, this is not possible for fixed tuned instruments (ney and similar) whose tuning is completed during the production phase. Fixed tuned instruments such as Ney were manufactured with different chords during the construction phase and to eliminate this problem. That is why ney has different sizes.
It is possible to examine the answer to the question of what are the ney types in two groups as "Main Harmony" and "Intermediate Harmony".