We present the latest developments of our work on the “blazar envelope” and the emerging hypothesis of the existence of a dichotomy of jet properties, with “strong” and “weak” jets, associated with jet (velocity) structure. The jet dichotomy does not match well with jet power being the sole fundamental parameter: differences in accretion mode (manifested observationally in the disc radiative efficiency) and BH mass play an important role. However, accretion power may only set an upper limit on the jet power.
Observations are consistent with a change in accretion mode at some critical value (in Eddington units) of around 0.01, linked to a transition in jet SED properties. A spectral sequence may exist in a “broken” form, and depending on the mass of the BH, jet of similar kinetic power may be “strong” or “weak”. The highest power “strong” jets exhibit collective evidence that their gamma-ray component external Compton (EC), i.e. they become dissipative within the first parsec. Lower power jets, though still very powerful and largely FSRQs (i.e. with luminous sources of soft thermal radiation around the jet), don’t exhibit a clear signature and may be consistent with SSC origin of their gamma-ray emission, hence larger dissipation distances.