[Fx82]

I'm trying to lower the rear axle of a F11 pre-lci. I use Ista but it doesn't do what it should be.
The car has 20"inch rims and I selected 20"inch. The front has been lowered 20 mm with springs.
Ista gives the following:
front axle: 657 mm
rear axle: 655 mm

When I change the rear axle to 675 mm it does lower it a little but there is a difference between left and right rear axle   
The first 2 times it did save the values after that it doesn't save them anymore. 

What is the right procedure to lower it? It should be easier than this.