Density clump: forward shock model with varying microphysics parameters. Synthetic light-curves at 2 eV (black) and 10 keV (grey) when the microphysics parameters of the forward shock are changed at the density clump: ϵ_e is increased by a factor 5 from an initial value of 10^-2, keeping the prescription . The Lorentz factor, injected kinetic power in the outflow, and the density distribution in the external medium are the same as in Fig. 3. The dotted and dashed lines correspond to the single and multi-zone models for the shocked region. The same simulations with the addition of a jet-break (assuming θ_jet = 0.08 rd) are also shown.