So yeah is pronounced yah where you are. Here it starts as yeh, then elongates into an 'ah' at the end. Not quite a distinct two syllables, but more elongated than a single syllable.

And I think I've only really encountered yea when singing hymns: eg:
Yea Lord, we greet thee
Born this happy morning...
I've never heard it pronouced yeh!

I do find accents interesting. Linguistics minor, not that you'd know it.