The development of intelligent assistants has largely benefited from the adoption of decision-theoretic (DT) approaches that enable an agent to reason and account for the uncertain nature of user behaviour in a complex software domain. At the same time, most intelligent assistants fail to consider the numerous factors relevant from a human-computer interaction perspective. While DT approaches offer a sound foundation for designing intelligent agents, these systems need to be equipped with an interaction cost model in order to reason the impact of how (static or adaptive) interaction is perceived by different users. In a DT framework, we formalize four common interaction factors -- information processing, savings, visual occlusion, and bloat. We empirically derive models for bloat and occlusion based on the results of two users experiments. These factors are incorporated in a simulated help assistant where decisions are modeled as a Markov decision process. Our simulation results revea...