DD spends most of its time creating full backups

I'm backing up to Rackspace with ~53 GB (uncompressed) dataset. Because my machine is a laptop that isn't always on, and because DD apparently uses bandwidth sparingly, a full backup takes considerably more than a week to complete. Then, it only does very few incremental backups before it decides to do another full backup. The upshot of this is that there's a full backup running on my machine nearly all the time.

I understand the reasons for periodic full backups, but I think this is a bit excessive. I'm paying more for data transfer into Rackspace than for storage. How can I tame DD so that it will spend a reasonable proportion of backup time doing incremental backups instead of full backups?

My backups are scheduled to run daily, and DD is configured to keep backups for at least a month.

Finally, despite the over-zealous full-backup schedule, the most recent backup I can restore is almost a month old. Why can't I restore to yesterday or the day before?