The width for the menu items is determined based on the menu that you are using in SiteAssist. You can use CSS Menu Writer to create your own custom menu that has a width that will work for your items. If you do not have CSS Menu Writer and need to adjust this manually you would do so by editing the following CSS:
home page
ul#cssmw_home > li > span > a {
content page
ul#cssmw_content > li > span > a {
In here it is the width setting that is responsible for the size of these items in the menu, you can adjust it to be whatever width you need.