On-axis radio light curves at ν = 4.86 GHz comparing impulsive Blandford–McKee (BM) blast waves with fallback-powered (FB) jet models. The FB simulations adopt the physically motivated jet luminosity histories shown in Figure 1. Results are shown for isotropic-equivalent energies of E_iso = 2 × 10⁵¹ erg (models labeled “b”) and E_iso = 4 × 10⁵³ erg (models labeled “a”). The two-dimensional calculations assume jet half-opening angles of θ_jet = 0.1, 0.2, and 0.5 rad. Relative to the BM solutions, the FB models exhibit systematically later and fainter radio peaks as a consequence of sustained energy injection. For the FB models, the two-dimensional jets produce lower on-axis fluxes than the corresponding one-dimensional calculations because the emitting surface is reduced in collimated outflows, with narrower jets yielding progressively lower radio luminosities.