argle.bargle on "[Plugin: FeedWordPress] remove or limit "syndication_item_hash" entries?"

FeedWordPress works nicely -- thank you!
But it quickly bloats the wp_postmeta table with "syndication_item_hash" entries -- like tens of thousands/week.
How can I:
1. Reduce the number of these entries in wp_postmeta?
2. Safely remove unused/unneeded entries from wp_postmeta?
If I remove all the syndication_hash_item entries, I have to go back and re-setup the feeds (they disappear). But that does enormously reduce the db size, and speeds up performance of the site.
I am using FeedWordPress to pick up content from 4 feeds, averaging a total of 5-10 items/day.
Thank you.

http://wordpress.org/extend/plugins/feedwordpress/