[A tedious description of various experiments, failing attempts to sort this problem omitted here.]
I note that Finder Preferences ---> Advanced offers 3 choices for searches, schematically:
When performing a search:
(1) Search This Mac
(2) Search the Current Folder
(3) Use the Previous Search Scope
[Another tedious description of more experiments omitted here.]
Just a moment... Selecting alternative (3) does the trick for me! I can now restrict the search directory to "Fum". I just need to:
a) Choose Finder search preference (3), which to my mind implements "Search the Current Folder" and NOT "Use the Previous Search Scope".
b) Interpret "Current Folder" as the folder open and at front.
Life is now good! <heavy sigh>