It could also depend on what the original codec was as well. A more efficient capture yields higher compression later. I got horrible compression after using my camcorder's pass-through signal-convert function to create the master AVI.
I don't recall exactly what bit-rates Rikter saw with mine, but he did tell me he saw it spiking into the 8-9 range.
I'd love to hear ISOMIX's musical score.