You should be able to accomplish this by going to 'Edit podcast' from the main screen and adjusting "Unfinished number to keep". The max to auto download feature is for podcasts that do bulk updates (Real time with Bill Maher is like this). They will sometimes push out 3-5 episodes all at once. For daily podcasts it should keep downloading all the new ones, deleting the ones that are older than the setting for "Unfinished number to keep". Also, it will delete any that are totally listened to before deleting any that haven't been listened to keep under the "unfinished" number.
Let me know if this isn't what you had in mind.
For more/quicker help make sure to check out the user manuals