Like an overt pronoun, a ZP whose closest overt antecedent is far away from it is harder to resolve than one that has a nearby overt antecedent.
a corpus study of our training data reveals that only 55.2% of the AZPs appear in the same sentence as their closest overt antecedent, and 22.7% of the AZPs appear two or more sentences away from their closest overt antecedent.