The extra space is actually the min-height
set to 164px (it’s like this by default). You can reduce the height and it should fix it. Take a look around line 1710 in your CSS and change it from 164px to around 90px –
.header-image .site-title a {
float: left;
min-height: 90px;
width: 100%;
}
You can adjust it more if needed.