I'm going to be brewing a robust porter this weekend and it will be my first all grain using darker grains. I'm sure this question has come up a ton, but should I add the black patent malt and the chocolate malt towards the end of the mash (like in the last 20 to 10 minutes) or mash it from the being with my base malt and my crystal malt (I'll be using maris otter for the base)? I know that adding them later will reduce the harshness of the roast character, but is this counterproductive for the style?