Hey Fredroxin,
As far as I’m aware, there’s currently an issue where the Navmesh is recreated each time you load a level, which causes the default properties to remain.
The way to handle this for right now is to add a supported agent and set the agent radius and other properties in that.
You can do this by navigating to Project Settings->Navigation System and adding a Supported Agent. If you set the radius there, you’ll notice that the agent radius will be set correctly after you build paths or restart the project if you’re not seeing the changes immediately.
Have a great day