Observed polarization degree (upper panel) and flux (lower panel) at observer frequency ν = 10¹⁵ Hz (PLS G) with a flat distribution of initial Lorentz factor (b = 0), smooth power law energy profile with a = 3.5, observed with q = 3. The structure of the magnetic field changes with the value of ξ. The direction of the polarization vector changes by 90° once the stretching factor ξ crosses 1, manifesting as a change in the sign of the polarization degree. The polarization peak happens at about the same time for all curves and is close to the break time of the light curve.