Jocool, it's always worked like a charm for me. I just dump about 3/4 of a chimney of coals into a pile right into the middle of the kettle, then fill the ring with corn (it's too crowded to put a full ear of corn in each slot, though you can alternate with potatoes or beets or whatever). The thing works like a charm, putting indirect heat on all sides of the corn-- no need to turn the ears or the lid or anything. It usually takes about 30 to 40 minutes for optimal doneness.
Duke taught me a sweet trick too: the corn-n-tator ring makes a great stacker. Put it on top of a regular grate, and then put an 18.5 grate on top of the corn-n-tator ring, and you've got double-decker cooking.