The UV adjust tool is very finicky, I only use it on boxes which have similar UV mapping to my object. So if my object is 100x100cm sort of unwrap, I apply 100x100cm box mapping to box, and use the UV adjust on that.
With Car Paints, you can get away with Triplanar though. Depends on individual scans as some with strong anisotropy get completely broken with.
Also, I think I ran into issues where carpaint had internally wrong scale I believe, could also be the case. It just looked wrong, same as you mention, unrealistically big.
In the end, the Car Paint even caused artifacts unless I massively turbo-smoothed the geometry.
Car Paints are one of the less great ChaosScans.. The fabrics are much better.