The role of velopharyngeal port opening (VPO) in the middle to upper voice transition in treble singers remains unclear, with conflicting evidence regarding its aerodynamic and acoustic effects. Empirical studies are limited and rarely compare Western Classical (WC) and Musical Theater (MT) singing. This study investigates changes in acoustic strategy, F0-nasalance, and nasal DC airflow during pitch glides on the vowel [a] using non-invasive, real-time physiological and acoustic measures. Nineteen treble undergraduate and graduate singers during the WC task used a statistically significant acoustic strategy in which the second harmonic (2f_o) exceeded the fundamental (1f_o) for the low pitch (C₅), with the relationship reversing at the high pitch (G₅). Fifteen participants during the MT task (A^b₄ to E^b₅) demonstrated a variety of acoustic approaches, including the WC strategy and two 2f_o-dominant strategies. F0-nasalance and nasal DC airflow decreased significantly from low to high pitch for the WC task, whereas no significant trends were observed for the MT task. These findings suggest that singers may employ VPO differently depending on singing style during the middle to upper voice transition, likely reflecting the differing acoustic strategies characteristic of WC and MT performance. Also significant was the discovery of a previously undocumented limitation to the Glottal Enterprises OroNasal 2-Chamber CV Mask used for the F0-nasalance and nasal DC flow measurements. While this limitation likely effected the F0-nasalance measurements for this study, the nasal DC flow measurements are unaffected. Future research will explore a correction factor for the mask, as well as obtain additional data for the MT task.