That is a good point and I like the visual metaphor of bad agents "floating on top of the pool". I was considering the fairly narrow problem domain between say

That is a good point and I like the visual metaphor of bad agents "floating on top of the pool". I was considering the fairly narrow problem domain between say 20 and 40 agents, and the queue fills up to perhaps 50 pending tasks mid-day. You are correct in the case that once you add enough agents to keep the queue empty, then additional agents reduce the fail chance. Sadly, though, the CI system I use (Teamcity) prioritizes agents that have a history of completing that particular task the fastest. That's great if your agents are all different specs, but fails spectacularly in this case, where a bad agent will be selected above a good one.