As the hip file I've attached, I tried to affect smoke size by pscale… Although looks it's working, but not the result that I want.

I want to get very keen and low density smoke at the head point.

How do I solve this?
Thank you.

Hello!
I had a quick look and it does seem to be doing what you want, but the radius for the “create_density_volume” may be rather large? It has a sample distance of 3.959…. you might also want to preview the setup with a Volume Visualization sop, and Volume Reduce sop (to find out the min/max density).

Interestingly, you are sourcing the fluid from itself, I didn't think a recursive loop like that'd work. I would suggest splitting the emission portion separately from the smoke sim would make it easier to narrow down your effect. While you do have mutual on the merge, the feedback scale on the pyro is at 0, so probably no two way interaction will occur.

Pop feeback with fluid is interesting, will have to try it tomorrow!