Fixation is a cognitive bias hindering creativity through the activation of previous knowledge. This phenomenon is well-known in the literature, as demonstrated by the many studies on actions to help individuals overcome fixation effects. However, these studies have often focused on individuals as ideators overcoming their own fixations and not on the ability of leaders to help ideators overcome their fixations. This study tested different factors, such as fixation heterogeneity (difference in fixations between ideators and leaders), design (having leaders design on the creative problem), and reading ideas of ideators, to understand their effects on the ability of leaders to direct ideators toward creativity using directive feedback. We set up an experimental protocol simulating an interaction between a participant, in the leader role, and a (computer-simulated) ideator, where the participant had to help the ideator to be more creative by providing directive feedback. An analysis of the results highlighted a phenomenon of rejection of certain ideas that were inconceivable for the participants, which led to better creative results for leaders not having the same fixations as ideators. This rejection phenomenon was significantly less important when participants were allowed to design without a reading phase before giving feedback.