Much of the formal linguistic research on third language (L₃) acquisition has focused on transfer source selection, with the overall finding that (global) structural similarity between the L₁/ L₂ and L₃ is the strongest predictor of initial transfer patterns. Recently, Cabrelli and Pichan (2021) reported data from the production of underlyingly intervocalic voiced stops in L₃ Brazilian Portuguese (BP) and L₃ Italian that highlight the notion that global similarity is likely moderated by other factors. Specifically, data from heritage Spanish/English bilinguals learning L₃ BP reflected reliance on (non-facilitative, but globally more similar) Spanish, while L₃ Italian data reflected greater reliance on (facilitative, but globally less similar) English. The current study is a first step towards identifying the source(s) of the disparity, in which we examine the roles of degree of dominance and explicit knowledge in heritage Spanish/English bilinguals. Thirty-four L₃ Italian learners completed a delayed repetition task in all three languages. We report English-like patterns that contradict the L₃ BP data and cannot be accounted for by degree of dominance or explicit knowledge. We connect these results to existing L₃ transfer accounts and the need for further consideration of linguistic and methodological variables, particularly acoustic salience in L₃ input and task modality.