You should use the 3 bars and check that still to 0, whatever the orientation.
Another solution for AuxMag orientation check, you can use the Scope with "Raw Magnetometer" and see if both mags (onBoard/external) are sync.
Go to the Scope tab, Windows menu > Edit Gadget mode and next choose the "Raw Magnetometer" scope.
Tip: Before switching to Scope tab, go to the Config > Attitude > Magnetometer tab for faster refresh rates.