I'd forget about the iceberg. To get a bit more light on the fall, playa little with the hardness of the cloud (in the main cloud tab), or the fractal (buoyancy from variation). Changing those values (buoyancy from 0.5 to 0.4, e.g.) may just make the difference. Or add a transform shader between cloud fractal and cloud node and move the cloud 10m.
I would also break up the strata in the distance by a ridged power fractal (larger number, say 50/400/10, and maybe stretched vertically).
Agree about darkening the moss.