Are you trying to use 75 ohm coax with a transmitter designed for 50 ohm?
If so you should be not be using the DiSlord impedance setting which changes the system impedance to 75 (or 77) ohms.
You want the SWR measurement to be based on what the transmitter will see.

The Tx does not see an SWR it sees an impedance, it is the transmission line that has the standing waves and that must be based on the impedance of the line NOT the load that the Tx 'likes to see'. The amount of reflected power will depend on the mismatch between the line impedance (75 ohms) and the impedance of the load. The design impedance of the Tx is irrelevant.

Leaving the settings at 50ohms may well give you an equivalent SWR of the impedance that the Tx sees, but tells you nothing about they standing waves on the 75ohm line. For Example, if a 1:1 SWR was indicated with a 50 ohm setting you might believe that there were no standing waves on the 75 ohm line, which would not be correct.

73
Jeff G8HUL