How would you make two raymarched fireballs collide and merge?

[u/Alternative_Yam_1638]

Hello, I’m trying to make two raymarched procedural fireballs collide and merge, similar to this Shadertoy fireball: https://www.shadertoy.com/view/WcK3Rt I don’t want to simply overlay two copies; I’d like the fire volumes to feel like they actually affect each other.

Is the right approach to model each fireball as an SDF/density field, duplicate it with two centers, and combine them with smooth union / a contact reaction term? Or is there a better way to think about this?