No accent mark for the 1st conj verbs in the 2nd pers pl. in the Pretérito imperfecto

[Nfqufktc]

Would you confirm my understanding as to why there is no accent mark on the verbs of the 1st conjugation group in the 2nd person plural in the Pretérito imperfecto de indicativo?
The accent mark is used in the 1st person plural

hablaba hablábamos
hablabas hablabais
hablaba hablaban

I checked the pronunciation in Google translate and indeed "hablabais" carries the stress on the senond syllable.

The rule says that words ending in -s, n and a vowel must be stressed on the last but one syllable. And the accent mark is used in hablábamos to maintain compliance with the rule
Would you confirm my understanding that -ai- in the bais represents a falling diphtong thus it cannot be divided?