does anyone know how to shut off Auto RX on a Canon Advance 500if w/ Fax board AM-1 Auto RX can't find user setting and T1 timer adjustment doesn't get it done. Is there an unpublished (specialB) NCU setting?

I have a new install, (2) two Canon imageRUNNER ADVANCE 400iF
Both systems are sharing a fax line. I need one to not receive.

I have adjusted in Service Mode the T.30 T1 Timer from 3500 to 9999. The systems are still not receiving faxes. If I unplug one I have no issues.
any insight would be helpful.