setting sys context in a data pump job

 I am  calling data pump to import files from a package.  The table I am  importing into has a column that gets it's value based on a sys context that I set.  When I run the dbms_metadata directly from SQL Developer the context gets set and the value is set. When it runs from  package the column is null.  What am  I missing?  Is it not possible to set the context in a data pump process?