If the captions are generated by Gemba and they do not allow you any control, then your only option may be to turn off captions generated by Gemba and put the captions on yourself manually, either in Storyline or in video editing software, like Adobe Premiere Pro.
Captions sometimes have to be moved in order to avoid exactly what is happening in your image, which is covering up something important on the screen. Again, if you have no control and can't move them, then you may have to make your own and then move them as needed. :(
