for the QL coals i use the larger 40mm ones, and i only use one at a time...this goes for any bowl style (clay, porcelin, glass, phunnel, etc...)
once the coal is lit i put it on the edge of the bowl anywhere, doesnt really matter where you start.* after getting the first puffs of smoke out of it (after around a minute or two) i move the coal directly opposite where it started and leave it there for around 10 mins, then just ash it and push it around the top of the bowl until it's dead and then start another one.
the reason i swap sides at the start after a minute is to heat up the rest of the bowl that has had no heat on it yet, once the whole bowl is warm it tends to stay warm as long as there is a coal somewhere touching the edge.
with the smaller QL coals, one seems to not give enough heat, but two sem to be a bit too much, especially if you have a smaller bowl. *if you use one full small QL and a half of another i've found that seems to work pretty well using the same method as above...or if you have a large (wide) bowl, use two small QL's and keep them 1/3 hanging off the edge of the bowl and that works well too.
for the squares or CH coals i use 2 or 3 and keep them evenly spaced apart (like a triforce
) and then rotate as needed.