Place of Supply Not Defaulting on Manual Tax Line

 We have e-Business Tax configured to allow manual tax lines to be entered in Receivables.  User enters all tax required fields and system calculates tax based on rate and line amount.  However, the system requires user to enter the Place of Supply for every manual tax lines entered.  I attempted to enter a rule to default the place of supply but user is still required to enter the Place of Supply.  Can anyone tell me how to get the Place of Supply to default?