To face the difficulties encountered by the mixed interactive systems designers during the design step, we propose a new approach for the design phase. This article introduces the articulation of an informal method, which is the focus-group, with a formal mixed interaction model. The articulation allows a better integration of the design step into the process and a more systematic exploration of the mixed interactive system domain. We illustrate this articulation by considering two mixed interaction models: ASUR and Mixed Interaction Model. Based on these two implementations of our approach, we carry out a com- parative analysis in order to identify the strengths and weaknesses of our approach.