This may or may not help, but...

The last time I did a car & flight booking on BA, it was to Norway. There was a big excess liability which I was covered for using a stand alone policy.

If I go to avis.co.uk and make a dummy booking, for Norway it shows an NOK8000 excess. For the US it shows a $0 excess.

I suspect you might find there is actually no excess liability. Agree it's shocking that this can't be confirmed up front however.