I'm not at all clear what you're asking, kenorrha.
Under what conditions is the bottom 1/3 of a slideshow shaded?
Are you using a theme or a template? Also, which version of the program are you using?
Welcome to the forum.
Can you post a screen-cap, showing your Timeline, one of the Clips with the shading and the Program Monitor, displaying this behavior?
Like Steve, I am not sure that I am clear on exactly where you are seeing this problem.
I think your slide show video has showing the letter boxing in top and bottom. You can avoid this only enlarging the image or video size.Please let me know the issue is different.