I know sweet FA about Cycles, BSDF and all that jazz, so I'll take your word on those. :D

I'm focussed on Firefly (as per the topic title - although this is as good a place as any to get a Superfly candle flame shader working too).

I think getting that three Russian-doll-style ellipsoids effect working in Firefly is 95% of what I'm after. It did involve fine tuning of some parameters and I need to annotate the shader network screenshot before I inevitably forget. As I put the shader together I remember first plugging the output of the N node (default settings) directly into the PoserSurface AmbientColor and rendering my flame. Realizing I just needed the vertical component, adjusting accordingly, rerendering. Realizing I needed to add an offset, adding a Math_Functions Add and plugging that into PoserSurface AmbientColor, rendering again, adjusting, etc. The two Math Function Gains and the EdgeBlend Attenuation were trial and error.

Perhaps I should do Firefly/Superfly render comparisons with various node outputs plugged into PoserSurface AmbientColor to see if I can identify a single node that needs a Superfly-specific tweak ? Or maybe I should forget about Superfly and let those who are familiar with it take the reins ?

The big thing I notice from your last three renders is that two of them have an almost horizontal divide between the orange-yellow-white zones, and the other has the nested ellipsoids the wrong way round - joined at the top, white smallest, inside yellow, inside orange largest.

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The 3Dcheapskate (also available in DAZ and HiveWire3D flavours) occasionally posts sensible stuff. Usually by accident.
And it usually uses Poser 11, with units set to inches. Except when it's using Poser 6 or PP2014, or when its units are set to PNU.