Subtle phenomena rooted in our body dynamics affect the reactive and evolutive parts of every human interaction. The authors' decision model allows for adaptive physical interactions between a human and a virtual agent. This article presents an evaluation of that model in terms of agent believability, the user's feeling of co-presence, and overall game experience. The results show that the model can generate adaptive body behavior for virtual agents that is comparable to a human's, but the user and agent roles in each scenario strongly impact the user's perception of the agent.