Watch the asterisk CLI, and you'll see the call bounce to/from AGIs as the Extensions execute.
After you find it, you can even turn on AGI debugging and get the information being passed. If you watch in the "screen", you can even see errors in the agi script if they occur (this is the ONLY place the errors occur unless there is a "try/catch" in the file, which there usually isn't).
Do note that each CAMPAIGN has a setting to keep a specific number of agents available ... however, I'm not sure how well that's integrated with inbound calls. It should be, but I've never tested it personally. If it's not ... it would be a better use of resources to repair that function (and submit a DIFF to the Issue Tracker) than to hard-code something into the inbound AGI script. Unless you put the same feature into the Inbound "No agents no waiting" and allow "XX agents no waiting" (With numbers ranging from NO to 10 in the dropdown).