No problem. :)
The problem with height is that it can't automatically grow. If you let a block-level element choose its own width, it will be as wide as possible. However, if you let a block-level element choose its own height, it will remain 0 pixels tall until it's made taller by its content. That's why it's easier to let the height be determined by the width (With the 'Shrink height if width shrinks' setting), or setting a fixed height.
A changing height also has the disadvantage of moving the content below it. This could become pretty annoying to the reader. (If you're basing the slideshow's height on the height of its images.)