Hi Juergen,
Good day to you.
I've finally solved my issue on the STO DO creation.
The ATP quantity is partially the solution, but another is SD configuration where Picking Location Determination were defined for my supplying plant.
With combination of Shipping Point ( from PO Shipping tab ), Plant ( Supplying ), and Storage Condition ( PO material in MM03 > General Plant / Sloc view ) data, source of Picking Location ( Sloc ) is determined.
Based on this, I know on which Sloc I should focus to and make sure stock is enough for DO creation.
Thank you Juergen for your help and the document you've shared.