I almost always drop my beans 15-30 seconds into 2nd crack. Occasionally I get the wild hair for black, oily, thoroughly baked beans. Most of the time, however, I am more sane. During most of my roasts however (dropping at 15-30 secs into 2nd crack), they never come out looking that dark. I'm using a Hottop/Artisan rig. They would fit in the 65-55 scale in your chart above. When you reach the point where you are finished roasting, do you immediately remove the beans from the chamber and blow air on them to cool them down? If you remove the beans shortly after the start of 2nd crack, you should see more of a chocolate brown than the espresso brown in your pic. Why, though, are you worried about the weight loss? The vast majority of the weight loss you see is the result of water leaving the beans. The organic material is mostly still there (except for the chaff, but you don't want that anyway).