Simple syrup is usualy made with a 1:1 ratio of sugar and water. That's the ratio reflected in this brown sugar syrup recipe. But yes, you could easily make a it stronger by using a 2:1 ratio of sugar and water. Syrup made with a 2:1 ratio is called Rich Simple Syrup. Alternatively, instead of making the syrup stronger...you could simply use twice as much simple syrup for similar results.