There is indeed and we have it reported already 
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Hi all, thanks for the discussion and examples. We understand that cloud rendering (and volumetric scattering in general) can work differently in different renderers. Some improvements are possible in Corona, but at this point we do not think they are critical to Corona development (creating ultra-realistic clouds / volumetric effects is not so common among Corona users).
If I am not mistaken, the realistic-looking clouds with strong silver lining or the darkening effect would require what we have already logged as a feature request under “blending several phase-functions in a single volumetric material”.
Currently, you can create with Corona a volumetric material which has uniform scattering (same scattering towards and away from the light source), forward scattering (more light is scattered further from the light source than bounced back into it), or backward scattering (more light is bounced back into the camera than passes further). This is controlled using the directionality parameter. What is currently not possible is blending those behaviors in a single material (e.g. a material which would have +0.9 and -0.9 directionality at the same time and this would be blended together) or using some special “curves” to define the scattering.
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Thanks so much for replying. I still think that this should be improved in both speed and behaviors ( using blending like you said ). It may not be a priority right now, but I truely hope it won’t be a long delay. Because today’s renderers are all very advanced and users are always demanding more and more for quality and volume is a very important thing.