I had that problem last summer when going to trackdays with the car loaded up with 4 wheels in the boot on 205 tyres, tyre would rub on the arch. I raised the car to solve the problem! I was going to get the arches sorted but thats a lot of effort compared to turning the spring platform round twice to lift the car! This was with an extra 1 degree negitive camber! But i think the problem was caused by the toe angles, wheel was rubbing the arch just above the side skirt.
Im on 195 tyres now and back down to the lowest setting and theres no rubbing at all. Camber might solve your problem but be carefull if you chane toe. best thing to do is not run such a large spacer, changing the spacer is probably a lot less ball ache than playing arround with the rear camber, wheel, caliper, disc and stub axle have to come off everytime you want to change it, which is why the race car shims are so easy as they do excalty what they say on the tin, playing with washers could take a long time.