Moesia Header Image Height Adjust

Hi there

Great theme by the way, great job.

I am having problems setting the height of the header image so that it only covers 50% of the screen (Instead of covering 100%)

I have my menu fixed accross the top of the page and I only want my header image to cover 50% of the screen (or an amount of pixels on a big screen, for me I need 420px)

When I test my page and inspect the header image, I find the header with class masterhead, with the height set inline to 846 (my screen height). If I change the height inline in the browser inspect I get the desired result, but I cannot find out how to change the height of the header image anywhere in all of the files in the theme folder.

I have looked through every css and function and I cannot find where the theme sets the height of the header.

Could you please advise me as to how I go about changing the height of the header?

Any help would be great.