In the cooking topics section of TVWB, it says that the charcoal measurements assume the use of an 18.5" WSM. How much should I increase the measurements for my 22.5"?
I believe it depends on what you are cooking. For ribs you can use a "snake" or "C" shape around the edges of the ring and have plenty for the short cook but for a butt you'll need more. As you gain experience you will be able to judge the usage of your cooker better. Until then, I recommend filling the ring and when done cooking shutting all the vents. Your cooker will cool down and preserve the unused fuel. You can tell what was burnt to get an idea. The leftover can be used next time.