Talking of Terragens scattering in clouds my understanding of the Fake Internal Scattering is that is single scattering in the forward direction only; whereas the lighting of real clouds comes form multiple Mie Scattering in both the forward and backward directions, also there is droplet optics to consider and the scattering interactions between droplets.
The thing is; that we will only be able to get so far with TG2 as specified and equipped the way things are today a case of close, but no cigar. These things may change over time but that's for the future [maybe]. In closing I don't wish to rain one any ones parade, just stating my two cents worth, and that's that.
Regards to you.
Cyber-Angel