Models are increasingly recognized as an effective means for elaborating requirements and exploring designs. For complex systems, model building is far from an easy task. Efforts were therefore recently made to automate parts of this process, notably, by synthesizing behavior models from scenarios of interactions between the software-to-be and its environment. In particular, our previous interactive synthesizer generates labelled transition systems (LTS) from simple message sequence charts (MSC) provided by end-users. Compared with others, the synthesizer requires no additional input such as state or flowcharting information. User interactions consist in simple scenarios generated by the synthesizer that the user has to classify as example or counterexample of desired behavior. Experience with this approach showed that the number of such scenario questions may become fairly large in interaction-intensive applications such as web applications. In this paper, we extend our model synthes...