Tried again with a slightly different type this time.
These work much better. I fitted them the other way round to the way they are meant to be fitted. This brings them away from the calliper and still fits inside the wheel. I then cut the rubber outer part of the disc so it would fit better in the wheel. Cutting was easy as there are indication rings at the edge of the disc allowing you to cut a nice even circle. I ended up cutting down 5 sets of rings on my 15" wheels.
Double checked when they were fitted and they are clear of the calliper, checked again after my trip to Swanage and everything is still good. No signs of wear or heat damage.