Fractional increase in magnetic energy, |$\mathcal {E}_{\rm mag}^{\rm str}/\mathcal {E}_{\rm mag}^0$|⁠, as a function of position of superconducting shell |$\mathcal {R}$|⁠. We consider a plausible range of values of |$\mathcal {R}$| in increments of |$0.05R_*$|⁠, and also the ‘fiducial’ model with |$\mathcal {R}=0.79R_*$|⁠. In the dimensionless units used in the calculation, the pre-condensation magnetic energy |$\mathcal {E}_{\rm mag}^0=5.4937$|⁠.