Why is svaha in Japanese sowaka?


I know this is a more Chinese centered question, but, if svaha sounds more
like suwaha, why is it transliterated sowaka? Or more straight to the point,
why is it that the Chinese word sowaka might have derived from, sa po he, and
in Middle Chinese I think sa ba ha, not suwaha, unless it didn't have those
syllables/the pronunciation of suwaha or the way it was heard varied. One more
part that connects to the question is how did those readings get converted
into so, wa, and ka (how did those Chinese readings convert into Onyomi even
though it's a more general question)

