Negative crash on GW chassis

I would like to ask you a question about the chassis species among you. My girlfriend drives a 225 TTR-Quattro with a KW chassis, variant 1. The chassis is screwed down to maximum at the rear, results in approx. -45mm !! Unfortunately, this results in a quite severe negative fall on the rear axle. This has led to the tires having completely run off after about 10,000 km inside. But only inside, outside they still look like new. KW says that you have to live with it because you can’t adjust the fall at the Quattros rear. How did you solve this problem? Or do you need all 10 tkm of new tyres? Gruss