Designers interact with a wide range of design tools, in a variety of ways, in order to support their work. Any attempt to produce digital tools aimed at supporting ideation raises the question of the kind of information considered account and what is appropriate to the needs and expectations of designers. We developed and implemented an assessment method for digitally supported conceptual design based on reflective conversation, flow, cognitive ergonomics and activity theory. Our approach opens up the evaluation spectrum to include parameters beyond performances factors for conceiving new digital design tools. This assessment approach considers user (the designer), action (ideation) and object (the tool) in the ideation process, namely the designeris experience interrelated to the needs of the task and the characteristics of the tool. In this paper we present the results of several research protocols in which we observed, analyzed and successively acted upon five different stages of the interface of a design tool as it was being developed, the Hybrid Ideation Space (HIS). Taken as a whole, these results suggest the limits and support of designersi optimal relationship with an ideation interface.