Sounds to me like you're just too low! It's the only real explanation for it to be catching on the outside on standard size tyres, unless it was the inside of the wheel touching the spring/adjuster, but i'm unsure on the spec of Octy Spider wheels.
I 5mm spacer will only make it worse if it's the outside of the tyre. All i can suggest is raise the coilovers a few threads, maybe 5.
I may need to do that