I don't know...
As I said, I don't know how to pronounce it exactly, but looking at the pronounciation key for
Sian, it's SHAH:N...
http://www.behindthename.com/pronunciation.php
Note the astrisks on
AH and AW and the ":" --- add an "a" at the end (like
Shauna) and how do you not get a possible pronounciation that is the exact same as
Shauna?