Comparison of photometric models to HST asymmetry amplitude A₄₀, minimum longitude ∆θ_min, and the PPS optical depth τ_pps measurements. Both identical particle (upper frames) and W = 20 size distribution models (lower frames) are shown, for various τ_dyn values indicated by the legends. In all cases ϵ_n = 0.1 andρ = 250 kg m⁻³ is assumed. Filled circles indicate simulations leading to overstability. The HST measurements are from French et al. (2007). Arrows mark regions where overstable oscillations have been observed in various studies quoted in the text.