Mountainous Area Cloud Base

According to the user guide:
"Cloud base: Cloud base height is the altitude of the lowest cloud base above the ground, especially important for pilots. The model of terrain is simplified, so be cautious to use these values in the mountains. On large areas, the forecast model is not able to calculate the cloud base."
I'm curious how the simplified the terrain elevation is calculated and what parameters determine the cloud base over the mountains. Does anyone know if it is a mean or average over an area? ie mean elevation over 5 square miles, or maybe the lowest elevation over a set area?
We do use windy as a data point for flying in the mountains and that data would help interpreting the forecast

@drrabazz
This article about ECMWF model may give you the information you are looking for on the orography model that is integrated into the weather model itself. Indeed the orography model corresponds to a coarse and simplified terrain profile.
All weather models use such a terrain model, which is generally more precise in high resolution weather models.
Then there is the effect of the horizontal resolution (9km), on the uncertainty. Here is an example in the Swiss Alps. The cloud base is at 0m in the purple square i.e. both above the Matterhorn at 4400m and above Zermatt at 1500m ! The square dimension corresponds to the model grid spacing.