Thanks for using the plugin,
The issue is this: the plugin is built to manage a wide variety of use cases, and is intended to show off as much of the picture as possible within the specified height. Height is declared in the widget to standardize the slide, as not all images used will always be the same height.
The slider is set to fit all slides into the maximum area that you set. This means that if it is set to 300px and one slide is only 200px high, that one slide won't affect the layout of the whole slider. What you will end up seeing however is that one slide set at 200px, with the controls still set as if the slide is 300px tall.
In a future version I'll try to fix this some, but it's mainly basically a feature, not a bug.