Currently, the values you use for maxImageWidth and maxImageHeight are limiting the size of your images within the gallery. Your gallery's dimensions are dynamic (changing with the size of the user's browser window) and in a tall browser window, the gallery's height will be large but the images will not be able to be scaled any larger than the maxImageWidth and maxImageHeight values, resulting in space below the images (as you use imageVAlign="TOP").
If you do not want your images to be displayed any larger, then the only way to reduce the space is to limit the height of the gallery, perhaps by setting the gallery's height to a fixed pixel value (rather than a percentage).
If you would like to have a header and footer of fixed height on your web page and have your SimpleViewer gallery resize to fill the remaining browser window space (with no vertical scroll bar), please see the Using a Resizable Gallery with a Header section of the Embedding Guide.
Check out the View Vertical Resizable Gallery with Header Example. You can download the sample (or view the source of the page in a browser) and copy/modify it to suit your own needs (by swapping the header and footer with your own content and replacing the sample gallery with your own).
SimpleViewer Support Team.