If it even works. It isn’t really a free-castoring wheel. It behaves somewhat like a free-castering tailwheel in the DC-3, but gets weirder the smaller the plane gets. This issue has been discussed thoroughly. Still, there is a belief it can be done via the flight_model.cfg. So far that isn’t the case, and we have been waiting two and a half years to be able to say otherwise. If it was, developers like FlyingIron wouldn’t have resorted to using custom code to simulate it (why would they waste their time?)
See: Make Castering nose / tail Wheels an option in Assistance Settings - #6 by Steinways. The OP attributes the odd behavior of the free-castoring wheel to the contact point not corresponding to the position of the wheel on the ground, leading to some strange results.