—Pairwise error probability (PEP) is an essential tool allowing to design practical optimized coding schemes. It reveals the connection between the performance and the decoding metric that is directly related to the codeword and/or constellation properties. The application of this principle to the hierarchical PEP used to describe the decoding performance of many-to-one message functions (hierarchical network code maps) in physical layer network coding (PLNC) is addressed in this letter. Unlike for the single-user case, the hierarchical PEP reveals a complicated dependence on the structure of the hierarchical codeword/constellation. The structure is defined in terms of hierarchical distance and hierarchical self-distance spectra. We show that the network coded modulation (NCM) minimizing the hierarchical decoding error probability should have zero self-distance spectrum leading to self-folded NCM design criterion.