"The elephant eats a tomato at the post office."
Translation:Fil postanede domates yer.
I thin it is better to say that you CANNOT place an indefinite object before locative (OR only place a definite object before a locative), hence you cannot say "Fil domates postanede yer" . You could have said "Fil domatesi postanede yer", if you were talking about a specific tomato
When you say domates it is automatically "a tomato" but when you add bir it becomes "one tomato".