Short description of error
i'm not sure what scattering function it uses, but esp since volume scattering is time intensive it may be productive to specify a more representative function such as in below esp if not slower
2013 Inverse Volume Rendering with Material Dictionaries: Supplementary Material (page11&12)
also maybe Rayleigh exact, mie?
for custom maybe even piecewise spline or linear-segments (unusual curves)