The Contact page in Kriesi's demo uses the Dynamic Template "Big Top Margin". What makes the difference between this template layout and the others is that Big Top Margin includes an element called "Margin below Main Menu" from which you select the Big Margin option.
So what I suggest doing is if you don't already have the Big Top Margin template under Flagship > Template Builder then create one using the settings in the screenshot.
Once you've done that go to Flagship > Theme Options > Styling, under the Header tab select "Upload custom image" to Background Image and upload your image to the Custom Background Image box that appears. If you want different images on different pages then you would need to upload the image to the Header Background Options box for each page.
Hope this helps!