This study aimed to assess how a user’s assembly process was impacted when a curved shape characteristic was added to a different position on the joint. An experiment was conducted with 30 participants who were asked to assemble three variations of the joint model with components similar to the geometric, centered curve design, and boundary edge curve design, respectively, as stimulus information. The participants’ assembly actions were recorded and statistically analyzed. The results indicated that the efficiency and process varied depending on the position where the curve characteristics were added as stimulus information, and the performance gap also varied depending on the participants. Thus, controlling the timing of cognitive transformation by curve characteristics to increase efficiency and ease of shape perception was considered significant for assembly tasks with similar components.