FOR THE LOVE OF GOD HOW DO YOU CLEAR AC EXPLORABLE GRAVELING FIGHT - Lovers Tomb

Our party tried tonight for a few hours. Thief/Ranger/Mesmer/Warrior/Elementalist. Levels 52/40/40/48/54. We tried multiple strategies. All out dps on the mounds. All out on mounds focus elites when they spawn. Killing first set of mounds then defending the crystal. Just defending the crystals. We never made it past 50 percent. I notices melee kept getting miss/miss/miss/miss while attacking the mounds and ranged would get obstructed. What's up with this? Is there something I'm not understanding. Thoughts? Discussion lets get it here!!