The acquisition of English vowels as an L2 is complex, yet most studies focus on static measures, with little attention to dynamic spectral cues like Vowel-Inherent Spectral Change (VISC). It remains unclear how language experience and length of residence (LOR) in immersion-rich environments affect perception-production alignment. This study examines Polish learners’ perception and production of /e-æ/ (DRESS-TRAP) and /i-I/ (FLEECE-KIT). These contrasts are challenging due to phonetic similarity and category overlap as predicted by L2 models. Advanced learners showed greater perceptual accuracy and more consistent production, especially for /i-I/, while /e-æ/ remained difficult. With higher proficiency, learners exhibited greater formant movement (20-40% of vowel duration), but LOR and language experience were not significant predictors. These findings provide insight into phonetic similarity in theoretical models of L2 vowel acquisition.