what you describe is correct and that behaviour isn’t configurable. I explained what I know from reading the code here (a bit annoyed - sorry for that):
I agree this is missing in the docs.
A workaround to get propagating deletes is using two folders where each end has precedence to overwrite / delete per rule.
RoundSync could be used to set something up like this, Syncthing has behaviour switches. Then there’s the free/commercial FolderSync.