Some info after a bit of testing. Moonbow’s immediate base damage is the same regardless whether it is charged or not. An uncharged arrow can be shot 6 times from full energy. Charging the arrow minimally will double the dot damage, and can be shot 5 times from full energy. Fully charging the arrow only increases the aoe radius and not the damage, and can be shot 4 times from full energy. So if you want to deal efficient single target damage you want to fire minimally charged shots.