Interest is raising around eXtended Reality Training Systems (XRTSs), which started to be considered as a credible option to train companies' workforce. Even though there is a growing body of literature on best practices and techniques to be adopted for teaching individuals how to perform a variety of operations (e.g., for assembly and maintenance procedures), there are also training situations which have gone mostly unexplored yet. In this paper, we propose and evaluate three different metaphors to face the key challenges associated with training procedures involving parallax-dependent tasks, i.e., tasks in which the instructor needs to make the trainee reach a target observation point and guide his/her attention towards a given point of interest at the same time. Effects observed through a user study that was run in a testbed environment indicated that metaphors based on 3D avatars and frustum visualization can provide important advantages over video-based techniques.