I doubt that finding, or preparing a flat patch of ground will be much of a problem outside of steep alpine or Big Wall terrain, where you would probably be better off with a hanging stove.

If you really want to carry something "for the fire cup implementation" little tripod gizmos are available, intended to enhance stability for cartridge stoves, that probably could be adapted. I prefer the Neanderthal implementation mode - "Ogg take rock, make ground flat, implement fire cup."

I do a lot of things in Neanderthal mode......
Geezer in Chief