OK, this works 🤦‍♂️

disk
{
  level           (1 2);
  faceZone        fz_disk;
  cellZone        cz_disk;
  cellZoneInside  inside;
  faceType        baffle;
}

I initially tried the ``faceType baffle`` but without the ``cellZone`` and ``cellZoneInside`` lines since it did not make sense to me to define a cellZone since I have only a surface