When you add as many feeds as you can from the list available, more feeds are then viewable. But this behaviour is not consistant.
When you add 3 less popular feeds (at the bottom of the list), the list does not expand to 20 again, it will simply stay at 17. However, if you add 3 popular feeds (at the top of the list) the list will expand to a full 20 again.
Due to the limit on subscription "costs", there's only so far I can look "down" the list before I run out of RSS credits.
But, as a result of this experiment, I have now added:
lonecat a blog
fishbowl_all a blog
theonering_net TheOneRing.net forged by and for fans of JRR Tolkien
rands_in_repose the digital opinion unit of Jerkcity Enterprises
joelonsoftware painless software management by Joel Spolsky
openbsd_journal Open BSD Journal
mrsnotnesbitt Arwen.org The website caught with its panties down
The lowest readership I've been able to get to display is a readership of 4.