The term „spatial-size association of response codes“ (SSARC) effect denotes the observation that people respond more quickly (and accurately) to a small stimulus with a left-hand response, and to a large stimulus with a right-hand response than the other way round. We explored the functional locus of the SSARC effect in two experiments. In Experiment 1, we investigated if the parallel processing of stimulus size and stimulus location can lead to interference (i.e. congruency effects) on a perceptual level of processing. The visual stimuli varied on three feature dimensions (i.e., color, size, location), and participants had to classify each feature in a separate condition. We didn‘t observe a congruency effect between size and location when participants classified color, a condition excluding S-R correspondence effects. In Experiment 2, we investigated if the SSARC effect originates on the same processing stage as the Simon effect, which has been shown to arise at the response-selection stage. The visual stimuli were the same as in Experiment 1, but now participants pressed a left or right key depending on stimulus color, setting the stage for SSARC and Simon effects to occur. An interaction between the two effects would provide evidence for a common origin (i.e. response-selection stage). In fact, we observed an interaction, but only for participants who also showed an SSARC effect in a control condition with central stimulus presentation. In sum, the results suggest that physical size and space interact at the response selection stage, but not at a perceptual level of processing.