It would be good to be able to use some temporary positioning constraints between objects in the model to accurately position objects. The translation tool does not seem to work in a way that is particularly useful as the point selection is pretty arbitrary and you cannot accurately select where the point is and what the distance relationship between the selected points should be for the translation.
Usually I edit the place of the start/endponts by sketches on the surface, and drawing an any kind of circle to that point. Then move the points of the start/end to the circlle , it will snap to the center
A little more time but work, and safety, and accurate.