How to calculate width of 28" tire to 26" with constant damping factor? Let's say you have a 28" tire with X width.

The question is how to calculate the width for 26" tire to get the same damping factor? I am looking only for solid solutions.

I will assume that calculating it backwards is simple reformulating the equation.

Update

"Solid solution" = "I tried it, I know it, so I say it".

Damping = it is like "user experience", you ride and either it feels comfortable or not. After all I hit both kinds of obstacles, rails for example and holes in the street (Poland is famous because of them). 

Tires -- what I have in mind, is exactly the same tires, same manufacturer, same type, etc. Currently I use 26" 2.35" (Fat Frank and Super Moto) tires, and I am wondering (approximately) what 28" tires would be the equivalent.
From my experience, dampening depends too much on non-dimensional factors. That makes very difficult to come with a formula that would work reliably.

Of course the width of the tire is a very important factor, and balloon tires always will dampen better than skinny ones.

But the hardness of the carcass (be it the layers within or even the rubber hardness itself, or the thread pattern) plays such an important role that I think it counts more than the difference in diameter from 26 to 28 inch wheel sizes.

I have ridden wide tires which were very bumpy and uncomfortable, and narrow ones that just made the harshness of the road disappear.

Also, and this might help to formulate a real answer to your question, are you referring to the transversal dampening, where the tire's cross section counts a lot, or to the longitudinal dampening, where the wheel diameter counts more - and which is responsible for "rolling over" obstacles being smoother on bigger wheels - ?