Hi,
yes, I think you are looking in the wrong direction.
"Example: when I do create an warehouse task in the way to remove any HU with /SCWM/ADHU, the source bin for predefined storage type would automatically be found with FIFO."
Have you tried that? What do you see in the transaction? A list of the HUs you have selected with the selection criteria. So the source bin is clear, because you select the HU.
Or I do not really understand what you are trying to do.
Brgds
Juergen