As from July 2019 – Sound generators will produce a specified level of noise when they are reversing or running below 20 km/h (about 12mph). The sound generated will be similar to that made by a conventional engine and can be temporarily deactivated by the driver if judged necessary.
It does not specifically suggest either way, that it includes stationary vehicles whether in a forward or reverse gear. However Hyundai/Kia cars like there bing and bongs, so as you suggest, will emit an audible sound when stationary in reverse.
Not much help really!