If I recall correctly, Ioas is LXX for Yehoash rather than YHWH.
There, -as stands for -ash, and theophoric part is simply Io. A common
ancient transliteration is Iao, which doesn't seem to me consistent
with Tiberian vocalization.
In Tiberian vocalization, schewa prior to He with seghol would be
pronounced as
a short [o] vowel. So rather than "Yehova" it would be "Yohova."
Similar
transliterations can already be found in the Septuagint. For example,
yhw)$ is
transliterated as Ioas.