RMS magnetic field strength (solid lilac) and the effective Alfvén timescale (solid orange) as a function of time for tracers in the Flat-TurbB simulation. Averages are calculated using all tracers that passed the shock before t = 10 Myr. The magnetic field initially experiences the expected level of amplification, but then subsequently decays. This decay is well-described by a simple model (Eq. F.1), which replicates the untangling of the turbulent magnetic field (dotted lilac).