It’s actually the hyperlink that needs to be adjusted rather than the image itself. Take a look around line 693 in your css file and change the width to around 300px instead of “55%”
.header-image #title,
.header-image #title a,
.header-image #title-area {
display: block;
float: left;
min-height: 225px;
overflow: hidden;
text-indent: -9999px;
width: 300px;
}