Sketch of the geometry (not to scale) assumed for the model. Seed electrons are accelerated in the gap and multiplied in and behind the gap through ADAF photons. For simplicity of drawing, photons are not shown in the in-gap and post-gap multiplication. After propagating away from the gap, the electron beam meets an emission-line photon field, driving a cascade, whose steady-state gamma-ray photon density is n_γ and whose escaping flux is F_casc. To convert n_γ into F_casc, cf. Eq. (3).