  Estimates of magnetic field strength in relativistic jets of active galactic
nuclei (AGN), obtained by measuring the frequency-dependent radio core
location, imply that the total magnetic fluxes in those jets are consistent
with the predictions of the magnetically-arrested disk (MAD) scenario of jet
formation. On the other hand, the magnetic field strength determines the
luminosity of the synchrotron radiation, which forms the low-energy bump of the
observed blazar spectral energy distribution (SED). The SEDs of the most
powerful blazars are strongly dominated by the high-energy bump, which is most
likely due to the external radiation Compton (ERC) mechanism. This high Compton
dominance may be difficult to reconcile with the MAD scenario, unless 1) the
geometry of external radiation sources (broad-line region, hot-dust torus) is
quasi-spherical rather than flat, or 2) most gamma-ray radiation is produced in
jet regions of low magnetization, e.g., in magnetic reconnection layers or in
fast jet spines.
