This paper investigates how directional asymmetry in Mandarin Chinese vowel perception differs across L2 proficiency levels in English-speaking learners. The study investigates the perceptual identification of six Mandarin Chinese vowels (/i, u, y, ) in dental, retroflex, and palatal fricative and affricate contexts by adult New Zealand English native speakers, using the Natural Referent Vowel (NRV) framework and the Dispersion-Focalization Theory (DFT). The results show that directional asymmetries are evident in the perceptual discrimination of the Mandarin Chinese vowel contrasts /y-u/ and / / among inexperienced, but not experienced, L2 learners. This suggests that universal influences (e.g., directional perceptual asymmetries) dominate during early non-native phoneme acquisition, while language-specific phonological adjustments become primary in later stages. To explain the directional asymmetry in the discrimination between two focal/point vowel contrast /y-u/, a new hypothesis: the Lower-Formant Convergence hypothesis, which is based on formant convergence, rather than peripherality in the F1-F2 space, was proposed. It suggests that vowels with convergence in lower-formants are more noticeable and stable compared to those with higher-formant convergence or no formant convergence. Furthermore, the directional asymmetry found in the perception of the pair / / represents a new perceptual directional asymmetry.