So you are using a non-powered Kemper with a 30w SS power source into a 1x12 cab with a Cel g112m speaker, with the CAB option ON which will enable you to use Pure Cabinet? If that is your scenario wouldn't you want to use an FRFR speaker like the Kone speaker or Cel F12-X200? Having the CAB option ON when using a non FRFR speaker will most likely not sound very good regardless of how you set the Pure Cabinet option. Unless of course that Cel g112m speaker is pretty close to an FRFR.
you can use "pure cabinet" option while cabin section off. There are two pure cabinet option in kemper. One is in the cabin section the other one is in the main output settings, and second one is general. Applies all output.