Interesting way of looking at it (as it were), though in principle if there was some other scattering effect specific to methane, I don't see why this couldn't

Interesting way of looking at it (as it were), though in principle if there was some other scattering effect specific to methane, I don't see why this couldn't dominate the effects of Rayleigh scattering. (as I've said in the other comments, I'm not convinced that such an effect actually exists)