Custom header image

Hi, I'm trying to place my own custom image in the header area of the theme. I replaced the mast.bg image and expanded the header region to accommodate the longer image. The only problem is that the suckerfish menu height is unchanged and my custom image protrudes under and below where the suckerfish starts.

How can I lower the suckfish menu to start underneath the new header image? I tried locating the code in firebug but have no luck. Could you please tell me the exact css line where to make this change. I CAN'T FIND IT ANYWHERE!

Thank you.