Trouble With Basic Playlist from Artists limited to catalog

Hello,

I'm having trouble getting valid results for some queries and I'm not sure if I'm setting it up right. What I'd like to do is input up to 5 artists and receive a list of whatever songs in my catalog are 'most similar' to those artists. For example, this query:

http://developer.echonest.com/api/v4/playlist/basic?api_key=XXXREMOVEDXXXX&bucket=id:CALBLSS14721C1C716&artist=Ingrid%20Michaelson&results=100&type=artist-radio&limit=true

never returns any songs by Ingrid Michaelson even though there are multiple songs in the catalog. There are about 1200 songs in the catalog. The same happens if I try a static playlist, too. Would you mind letting me know if I'm doing something wrong -- or if there is another approach I should try?

Thanks for your time -- I'm really loving the API. Such cool stuff and it's so much fun to play with.