«أَنْتِ طَالِقٌ فِي دُخُولِكِ الدَّارَ»
“You are divorced upon entering the house.”
Fi does not simply locate a divorce inside a building. It connects the effect to the act of entering the house. The legal consequence therefore does not arise before that act occurs.
The particle here approaches the meaning of a condition. Compare the unrestricted spatial phrase “divorced in the house” with “divorced upon your entering the house.” The latter specifies an event on which the ruling depends.