You're probably right about the header size once the scrolling has begun especially on a mobile device, I think it should be shrunken.
I'm in the the process of changing the layout again. I'm thinking of switching to a one page layout with a bit less text. I've decided to focus on microsites, basically local small business and individuals websites. I'm a one man team so I can't created large time intensive web applications and websites, it'll take me months. I hate creating websites for myself, I'm a tough client. I'm thinking creating website packages is better for business since clients can have an idea of how much it will cost them all included. The only thing I'm having trouble with is getting enough clients. Maybe a blog on newbie stuff would help my Google ranking.