Hi,
First, there is a custom CSS rule, which forces the min-height of the results box to 100%, please remove it, as it will conflict with the height caluclation:
#ajaxsearchprores1_1 {
min-height: 100%;
}Then, since you have a very nice fixed header search, you can try a different custom CSS:
div.asp_r {
height: 80vh !important;
}This will adjust the height relative to the viewport height.