Left: Phase space diagram of magnetic field strength versus gas number density for our Mach 3 Flat-TurbB simulation. Contours cover 25%, 50%, 75%, and 95% of the probability density (represented by darker to lighter shades, respectively). Blue colours indicate the initial upstream distribution, whilst red colours show the final state in the injected region at t = 250 Myr. A cross marks the median of the distribution. Right: As previous, except data are taken from the Mach 3 fiducial simulation. Dashed lines indicate the empirical scaling of the 75% boundaries. Amplification is weaker than the naive expectation for Flat-TurbB due to magnetic decay. Meanwhile, for the fiducial simulation, amplification is significantly stronger than that possible from compression alone.