Test particle velocity diffusion coefficients for ν = 10 ³ c _s / L for three different β, corresponding to the non-resonant regime discussed in Section 2.2. Scatterers are stationary in the fluid frame. The results are similar for low β ≲ 1 where slow modes dominate the compressional fluctuations. For β = 10 the diffusion coefficient resembles the β = 1 results at much lower scattering rates (see Figure 3). This is because the compressional energy is significantly lower in the β = 10 simulation, which decreases the efficiency of the non-resonant diffusion.