Mixing Tamiya Smoke + Future. Do you add dish soap, too?

Actually, it is a wetting agent, which decreases the surface tension, but I agree with all the rest.  A small drop of good, pure white vinegar or other source of acetic acid should work also.

The soap increases the surface tension of the liquid, which should help it distribute itself evenly on the surface.  I would use it, myself.  I've been adding a drop to glazes I make from water, Future, and acrylic colors.  Future alread has a little better surface tension than plain water, but the soap helps the glazes go and stay where I want them.

Hello!

I was tinting canopies of my OH-6s some time ago and I've found that it helps a lot to thin smoke with water and apply several coats to get nice, even tinting. As for shading I'd say try to thin it first and see if it does the job. Then you could compare the effects with some soap added. But we're talking minimal amounts - if you add too much, it could negatively affect the adhesion of the paint.

Good luck with your build and have a nice day

Paweł