DIY – Internal Rear Sway Bar for IRS or Swing Axle bagged or coil sprung cars.

[dd-ardvark]

I see your point of concern. At first read of this concept, one would think that because you have two different lengths and diameters of bars that one side would flex more than the other.
Yes, is the answer to the smaller dia. bar flexing more, No is the answer to one side reacting differently than the other.
It may help to get the torsion bar idea out of your head…, envision just a bar of the same dia. passing from one side to the other and attaching to the torsion plates.

- Ask yourself this, what’s it pushing/reacting off of?

After you pondered this, look at the drawing…, and hopefully I’ve drawn this understandably enough that it conveys that the two bars are now mechanically one bar…, different sizes mind you, but again one bar.

With this said, hopefully you see that the answer to the pushing/reacting question above, is that your leverage point works off the other wheel, no matter if the bar was tapered from one side to the other.