I think I already understand what you want.
Just to be certain:
if you create the TO manually is it then the same bin for all items, or is it just equal to the FM behavior?
What happens if you overwrite the determined bin of the second item with the bin that is used in the first item? does SAP then issue a warning or error?
What is actually your putaway strategy and how is the storage type defined, is it just next empty bin? is addition to existing stock allowed? what indicator is used for mixed storage?