Flux-normalized relative magnetic helicity in the box vs. time for the key runs analyzed in this paper (absolute values are shown). The initial helicity of Run S is scaled, placing it in the middle between H₀/F² for Runs T2 and T3 based on the similarity of the parameters. The length unit and resulting Alfvén time of Run S are rescaled from the values in Kliem et al. (2013) to conform to the choice for the other runs here (the apex height of 0.1 R_⊙ at the onset of instability is used as length unit). The curves are labeled with the respective values of the ratio of external toroidal (guide) and external poloidal (strapping) field, B_et/B_ep, decay index, n, at the initial flux rope apex, and twist averaged over the cross-section of the current channel, Φ. The range of the conjectured base level of the mutual helicity in the configurations T1–T3, ≈0.06 − 0.08, is shaded in light blue.