Far shadows for Movable light?

Sorry, it might be a dumb question, but i had some hard time setting up Far shadows, for Movable light (Sun).
I want to use a short dynamic shadow cascade distance (5000 units), for better shadows on character.
But when i’m trying to use a single Far shadow cascade (until 15000 units) - it doesn’t do anything. In the result - all shadows are completely disappearing in around 100 meters from the camera.
What is the problem, maybe i’m not doing it right? Thank you!