Control How Much an Image Shrinks when the Header Shrinks

I created a header through Themer and turned on shrink. I like the shrink setting and want to keep it, but my image on the header shrinks to an unreadable size. Is there a way to control the size of a photo that is on the header when the header shrinks. It needs to be about double of what I am seeing now. Here is the site if you want to see the issue:

The bottle cap logo shrinks way too much when a viewer scrolls down. I used the UABB photo module for that image.