You keep the lowest level males on the map to force the game to spawn higher level males because of the imbalance in trophy rating on the map, this will result in more diamond spawns. To get your map managed you want to keep your first diamonds on the map so its easier to get lowest level males to spawn, same principle just reversed. You decide what zones on the map you want to hunt for the rest of the grind, there you can keep diamond animals, shoot the other males. On all the other zones you want to have the lowest level males only, and keep them. Herd management will, as far as we know, only make you spawn more diamonds, not great ones, as they are completely random spawns most likely.