The synch rule is tighten with data tables. The synch rule works when the data tables it associated with have certain data changes.
For instance, you defined a rule A, and table b, and c. you associated rule A with table c only. Now, you add table b to the form f1 which table b will be displayed as a grid b, and you add table c to the form f2 which table c will be displayed as a grid c. If you update the grid b and run the synch rule A, nothing will happen as grid b == table b and table b is not associated with synch rule A. While if you update the grid c on form f2 and run the synch rule A, the table c will be updated accordingly.
For individual fields, if they are on the subforms of form f2, like update, new form, and the fields are associated with data fields in the table c, run synch rule A will update the table c; Otherwise, the changing fields value wont trigger any data change on table c, and run synch rule A will happen nothing.