Right, keep it simple, and a good rule in your query is to not apologize for selecting them, don't apologize for your lack of previous publications, and above all, don't apologize for the story. I have reservations about the length of my story, I say something like "this is 240,000 word story that takes the reader on an epic journey of 17,000 miles across three continents." Because most want to know the word count, and I follow this with an explanation that it is a long story because it is a very long trip. Hopefully they will be interested in how this happened 2000 years ago. Many polite declines, indicating the query at least got read. On the other hand, only one request for manuscript so far! I recommend querytracker.org, which has about 1400 agents listed, and that site cannot get as fine-grained (humorous science fiction) as you have been trying. I agree with @terobi, just query SF, and in your query identify the target audience.
