I have little STEEM, so I'm afraid I have to do one offer at a time now, since I don't think I can offer the same STEEM more than once and just cancel the others once one is filled. But for the long run I think this approach you suggest is ideal. Split the available STEEM into 3 offers that are spaced one day apart, and have slightly different APRs available in each one.
This is so fun!