Saw it again on 15/11/2015.
I think it is Oriental Reed warbler.
Sorry for bothering.
Still find it smaller than Oriental Reed warblers I have seen before(more than ten times).
Quite "shy", seldom goes to the top of the reed.
No call.
But must be greater than Scaly-breasted Munia.
Length is comparable to Plain Prinia.
Body is "thicker" than Plain Prinia.