Sometimes it's more important to control the size of the view than the scale. There should be a parameter that controls the size of the view (in sheet space), and then the scale should be automatically determined.
There should be a different (set of) parameter(s) for IvBalloon that "simply" allows the balloon to be connected to the nearest drawing-curve. Currently, the user must name an edge and that edge must resolve to a drawiing curve in the view -- difficult to get this right. For IvBalloon, the easiest solution is just to allow a value of :Nearest for the "entity1" parameter.