Possibilistic Defeasible Logic Programming (P-DeLP) is an argumentation framework based on logic programming which incorporates a treatment of possibilistic uncertainty at object-language level. In P-DeLP, the closure of justified conclusions is not always consistent, which has been detected to be an anomaly in the context of so-called rationality postulates for rule-based argumentation systems. In this paper we present a novel level-based approach to computing warranted arguments in P-DeLP which ensures the above rationality postulate. We also show that our solution presents some advantages in comparison with the use of a transposition operator applied on strict rules.