Jon, 3/4 to a full chimney is fine to run in a 22.5 Weber kettle. Remember you control your heat with your vents, the more there open the hotter the fire(more oxygen to the coals) the reason you where low on temp was most likely because your top vent was only 1/4 open, that will smother the coals fast.
Next time when you start try using 3/4 to a full Weber chimney and dump them in the grill when the smoke stopes and flames are just starting to lick out of the top of the chimney. If you wait for the top coals to become fully ashed over the bottom coals in the chimney will be spent! Also start with all vents(top and bottom) wide open and you will get high temps. When you want to start backing the heat down start closing the bottom vent a little at a time, and try to regulate the temp with the bottom vent and leave the top vent open. Once you get comfortable with it you can choke the top vent down a little if you wish but I would never close the top more than a third. Almost all of my cooks the top vent stays wide open and I adjust me heat from the bottom. Only when going real low and slow(like 225) I will choke the top vent down. Hope this helps.