You can resize and reposition both the Hero Image container and the Image inside that (by double-clicking the Hero Image).
Although your Hero Image size/position is fixed for all the images in slideshow, you can definitely move/resize the actual images inside individually. See if that helps you get it to work for you in the Slideshow itself.
Else you can always for go the Composition Widget which allows you to place individual target slides in different positions and have different sizes.
Cheers,
Vikas