How are losses applied to a fort when the units in its space are eliminated?

Question

Accepted Answer

The fort takes losses last, after the defending units and any corps that replaced eliminated armies are gone. It is destroyed only when the leftover losses reach its Loss Factor, because a fort has a single step. A fort is never reduced by a combat its own side makes, and enemy forts can be destroyed but not captured.

Paths of Glory

How are losses applied to a fort when the units in its space are eliminated?