I'm sorta stumbled on this meaning here. "A skill level that can touch over the top of my head"?
頭上 generally means the space above the head rather than the top or surface of it.
I am not sure about this expression 頭上をとる itself, but I think it means "to move around to the space above the head of the other" in analogy to 背後をとる "to move around to the rear (of the other/enemy in fighting etc)". 背後をとる is a technical expression mainly used in areas of fight, battle or sports.