most suggestions here are special cases of perception based stealth system and not just a skill controlled one.
The rest is a matter of how much detail (aka work) you want to put into it.
Many games use a very simplified system, which usually leads to ridiculous perception ranges and a combined sense range.
If KCD uses at least distinct senses, e.g. seeing and hearing, with different factors - viewing arc, hearing different range than seeing (in the field of view), visibility/audibility of your gear, that would be a nice start.
Of course, if you want to put extra points into it, also add modifying factors on the viewer side (alertness (can be a combined variable for many things), environmental factors (ambient noise, light conditions, crowded vs. you are the only thing that moves ) )
And if you have still time, add a sense of smell and then try hiding if you haven’t washed in weeks - also nice for social occasions.
(works also in the other directions, hiding in a dung pile might work if no one is willing to look there)
The advantage of separate senses is, you could add them incrementally if you don’t decide on a combined model in advance.