Cognitive control has been theorized operating through two distinct mechanisms, proactive and reactive control, as posited by the dual mechanism of control model. Despite its potential to explain cognitive control variability, the supporting evidence for this model remains inconclusive. Prior studies frequently employed the Stroop task to assess this model, manipulating the proportion congruency (PC) at the list-wide and/or item-specific levels to target proactive and reactive control, respectively. However, these manipulations have been questioned as they may invoke low-level associative learning instead of control-driven mechanisms. Although solutions have been proposed to address these concerns, they still have limitations and impracticalities. In pursuit of a clearer understanding of this issue, we manipulated proactive and reactive control simultaneously to more directly investigate their separability. We conducted two experiments using a peripheral and a perifoveal spatial Stroop task version, respectively, and we adopted state-of-the-art methodologies, leveraging trial-level multilevel modeling analytical approaches, to effectively estimate the Stroop effect and its control-related modulations while controlling for confounding factors. Notably, we manipulated both list-wide and item-specific PCs at the trial level, allowing for a fine-grained analysis. Our results provide compelling evidence for the existence of a list-wide, PC-dependent proactive control mechanism, influencing Stroop performance independently of reactive control and confounding factors. Additionally, an item-specific PC-dependent reactive control effect was found to influence Stroop performance only in interaction with proactive control. These findings contribute to a better understanding of the interplay between proactive and reactive control mechanisms, shedding light on the intricate nature of cognitive control. (PsycInfo Database Record (c) 2024 APA, all rights reserved).