I would like to understand the difference in distribution between the alveolar consonants s, ts, tsʰ and the alveolo-palatal consonants ɕ, tɕ, tɕʰ in Cantonese. One source told me that the postalveolars are only used before i, y, and œ and alveolars everywhere else. I listened to a few sound clips to see if this was true and I found some conflicting evidence in these examples.
凈 [tsɪŋ] 傷 [sœːŋ] 坐 [tɕʰɔː]
Is there any set of rules that fully describes where sound is used? Also, how much variation is there among individual speakers?