Hi @Jen5 and @Lizzie
I think I got what you are saying without looking at the screen shot...
You want the search results to show big houses to small groups.. Because they might want to book big houses as a luxury "item" of their vacation... Is that it??...
This is not a problem... but a "feature"...
Indeed Airbnb will prioritize the right house for the right group..
their search engine is much more than you see, maching hosts with guests, hosts preferences and likability of the guest renting that specific house...
You are seeing the small houses first because the area you are serching have a lot of houses that won't fit in just one page and the search engine is prioritizing the houses with a larger chance to be rented by that small group, and with that doing that lots of happy guests quickly found the right house right for (or so the system and programers think this is the right thing to do it)....
try to zoom-in to a more specific area of your search or do a search to a area with less listings you you will see all listings that will fit 1 guest.. If you select 6 guests (and over) than it will start to eliminate the smaller houses that won't fit larger groups (but not the other way around, it does not eliminate the larger houses for a small group)...
This is good reading material on the subject
http://nerds.airbnb.com/host-preferences/
http://nerds.airbnb.com/search/
http://blog.airbnb.com/how-search-makes-the-best-matches/
http://blog.airbnb.com/understanding-your-hosting-activity/
Please take a look on my pictures... the 1 and the 6 results are the same... only they changed the order so the smaller house shows first, for the 6 group it show a larger house up top because a 6 group will likely rent a larger house than 1 person alone. The 12 group eliminated the houses that won't fit this group...