@Michael Buen I see where you're coming from.
However, please look at other characters that end with -ia:
加 jiā ㄐㄧㄚ
俩 liǎ ㄌㄧㄚˇ
掐 qiā ㄑㄧㄚ
虾 xiā ㄒㄧㄚ
It is pretty clear that -ia is just ㄧㄚ . There is no need to use two ㄧ. (Chinese phonology does not distinguish between bi-ia and bi-a.)
Therefore, biā should probably be ㄅㄧㄚ.
On a second note, I have never ...