The radial extent of the FeCZ is quite substantial, i.e. a significant fraction of one solar radius, which corresponds typically to 2 - 10 pressure scale heights, comprising a mass on the order of 10\(^{-6}{\,\mathrm{M}_\odot}\) to 10\(^{-5}{\,\mathrm{M}_\odot}\), while the amount of mass between the top of the FeCZ and the stellar surface is around several times 10\(^{-7}{\,\mathrm{M}_\odot}\) (cf. Table 1). In the 20\({\,\mathrm{M}_\odot}\) model the upper border of the FeCZ is located at \(\tau \approx 140\) on the ZAMS, and at \(\tau \approx \) 370 on the cool side of the main sequence band. In the 60\({\,\mathrm{M}_\odot}\) model the upper border at ZAMS is located at \(\tau \approx \) 15, reaching \(\tau \approx \) 260 during the late main sequence evolution. Convective velocities predicted by the MLT are on the order of 10s of \({\, {\rm km}\, {\rm s}^{-1}}\), where more extended zones achieve higher velocities. For a quantitative analysis, we define an average convective velocity where \({\mathrm{R}_{\mathrm{c}}}\) is the upper boundary of the convective zone, and where we set \(\alpha = 1.5\).