Make Header Image the Same Size in ALL Pages

Hello,

I am quite pleased with the Arcade Basic theme. I just have a little issue about the header image. I’ve noticed that it displays in full on the homepage like THIS, but is smaller in internal posts and pages like THIS.

Is there a way to get it to display in its full size in posts and all internal pages, too? I’ve been looking through this forum and a lot of people seem to have the same problem, but there have been no real fix for this.