In short-term serial recall, similar-sounding items are remembered more poorly than items that do not sound alike. When lists mix similar and dissimilar items, performance on the dissimilar items is of considerable theoretical interest. Farrell and Lewandowsky [Farrell, S., & Lewandowsky, S. (2003). Dissimilar items benefit from phonological similarity in serial recall. "Journal of Experimental Psychology: Learning, Memory, and Cognition," 29, 838-849.] recently showed that if guessing strategies are controlled, dissimilar items on mixed lists are recalled more accurately than on pure dissimilar lists, a finding that challenges several current theories of serial recall. This article presents two experiments that extend the generality of the mixed-list advantage for dissimilar items and then applies three theories of memory--the primacy model, SIMPLE, and SOB--to the data. The simulations show that the data are best explained by the SOB theory [Farrell, S. (2006). Mixed-list phonological similarity effects in delayed serial recall. "Journal of Memory and Language," 55, 587-600; Farrell, S., & Lewandowsky, S. (2002). An endogenous distributed model of ordering in serial recall. "Psychonomic Bulletin & Review," 9, 59-79.] which, unlike most other current theories, posits that similarity has an effect at the time of encoding.