زَيْدٌ فِي الدَّارِ: Zayd is the first-position mubtadaʾ.
فِي الدَّارِ زَيْدٌ: the prepositional predicate is fronted and Zayd is the delayed mubtadaʾ.
The core location remains the same, but the discourse emphasis may change. Zayd remains nominative in both.