Males pursuing alternative reproductive tactics (ARTs) face uneven sperm competition and are predicted to invest differently into ejaculates and mate acquisition. A still neglected aspect of ARTs concerns the potential influence of the fertilization environment, which may lead to deviations from classical predictions. Loliginid squid females have two fertilization sites (buccal membrane, BM; oviduct opening, OP) associated with ARTs. Dominant consorts are predicted to monopolize paternity –due to the use of a spatially advantageous site (OP)–, making it difficult to understand the maintenance of the sneaker phenotype, which curiously invests less sperm per mating. Here, we empirically evidence that fertilization sites indeed influence male success. However, females often use sneaker sperm stored at the BM to fertilize part of their progeny, highlighting the importance of the BM not only for sperm provision but also on how sneakers might persevere in a system dominated by consorts. Together, these results indicate that loliginid ARTs reflect complex fertilization dynamics, with consorts displaying agonistic behaviors to control paternity, and sneakers mating promiscuously to assure cumulative reproductive success, enhanced by long-term sperm storage. Ultimately, these results corroborate the importance of the interplay between fertilization environment and sperm competition in the evolution of male ARTs.