Question on sway bar set up

[Xan]

I was looking at the offerings from the vendors on sway bars and saw that they all increased the front a whole lot more then the rear.

I'm assuming these increases are against the stock set up. Now the stock set up is set for understeer, as almost all production cars are. So to get a good "race" set up you would want to bring the car closer to neutral with a slight under or over-steer depending on track and driver.

As the stock set up seems to be a bit soft in the rear, the car would benefit from an upgrade to reduce the body roll and keep the wheels on the track. So granted the stiffer set up would keep the wheels better planted and help with traction through corners, but why don't these kits come with a more neutral setup?

It seems to me that if you increase the fronts by over 200% and the rear only by 70% or so, you actually increase the understeer.

Or does the same percentage increase have more effect on the rear than it has on the front? And therefore you need less of an increase to the back to accomplish the same? If this is true, can anybody tell me the ratio for this?