I can see and access a large portion of the drops on my bars with bar mitts on, but there's no trick involved, they're just older handlebars with a longer and deeper shape than the modern compact bars in your picture. As Ghazmh says, if it's cold enough to need the bar mitts I almost never use the exposed parts of the bar anyways... the pogies also block access to the brake levers from the drops so there's that issue too.