Here is the Terragen campfire example. Scales are at 50cm (and even slightly under 50cm for placement and masking some boundary flames), which is actually a bit under scale, but for example purposes it works nicely, especially pushing Terragen's Ray Tracer to catch as many voxels (?) as possible.
The scene is built at 0,0,0 for ease of example, though the flames can be translated via the cloud layer position and Fire Position shader. The Flame Density Fractal seed is an easy way to get a new flames. You can also play with the Flame Warper seeds, though I'd be careful, it is easily bugged to create noise if not perfectly smoothed. I look forward to seeing your fires. Especially those with paid Terragen and optimizing it for a "usual" Terragen render rather than trying to obtain better quality above limitations.
Render time on the example scene image is about 1h 20m. You may be able to get away with less internal cloud quality of GI with higher [than 6] AA.
As a note: I do not intend any of my work for commercial use or gain without explicit permission from myself. These are for personal, and educational purposes.