I get it. What @jonwright describes is excessive. I'm guessing they live in a very hilly or mountainous area, which cruise control systems in general don't like and don't work as well as on flat roads. There's certainly room for improvement (adjustments). Obvious first step, and may help. But it's setting up sensors to allow it to react better for the coditions they encounter, not really fixing the underlying reactive nature of the system.The problem is that it doesn’t even reactively respond in an over speed scenario. It just lets it happen.
As @Stan-qaz just described, even when working "properly and acceptably," it still may require manual inputs from the driver from time to time. (Sounds like a fun AZ-MT trip)