It is my experience that insurers don't understand it either. I have received countless letters, phone calls and emails because I put a voluntary excess on my policies which, added to compulsory, totals my valuation of my car. They usually ask why am I doing this, and have a great deal of difficulty understanding that I do not intend driving like an idiot, so will not be claiming my damage from my own insurance, so if it reduces my premium - great.
I like your first sentence.😀
But have you tried to claim excess (Uninsured loss?), the body shop's usually have to recover the excess before they will release the car, then the insurer (in my case) claimed the case was closed they had paid for the repairs, next it was excess (£150) was not recoverable.
After a lot of toing and froing, I asked if they had the Ombudsman's address, and the cheque was in the post.