Two more I've come across.
The holes where the standard grate handles are allow for putting more coals in without lifting the grate up (from the 70's cookbook).
With regular briquettes, and the lid on the grill is designed not to get over 450 degrees no matter how much charcoal you have in it (temp is regulated by the limited airflow). To get closer to 550, tilt the lid slightly to allow more air in. For searing, remove the lid and let the coals get very hot.