The application of the high B mode concept has allowed an effective upgrading of the superconducting electron cyclotron resonance (ECR) ion source SC‐ECRIS, which is now one of the best operating ECR ion sources in the world in terms of highly charged ion production. To increase the high charge state intensities and the total extracted current we tried to enlarge the plasma volume, but no clear evidence of volume effects was substantially achieved. We also tried to increase the magnetic field of the trap. The theory which led to these experiments is outlined in the following along with the results of tests using larger plasma volumes and tests with larger magnetic field. Even if the theoretical basis is not always well established, the beneficial effect of magnetic field enhancement on ECR source performances is confirmed. The capability of superconducting ECR ion sources to get higher results with respect to room temperature source by means of a higher and variable hexapolar field is underlined. ©1996 American Institute of Physics.