If I may speak my mind, I really liked the image of your second post (http://www.luxrender.net/forum/viewtopic.php?f=10&t=5057#p52619
), because until now there was NO way to get a similar effect in Luxrender, nor in Maxwell Render for what I know.
(BTW it is what is called "Fresnel effect" in Cinema4D).
I do not think that the current implementation achieves the effect that "you get most light where you are viewing the flame along an edge, rather than looking face on" (or absorption, or diffuse, i would say), as it clearly appears in that image.
just my two cents.