Increase number of entries in og_my_block

I administer several groups on my site and have found that the og_my_block block seems to allow only a fixed number of entries: 5. After the first five groups appear in alphabetical order, all subsequent groups simply do not appear in the block.

I tried to configure the block from the administer blocks page in order to increase the number of items the block would show. But for some reason the option is not available. I've scoured drupal.org and find lots of tweaks for og_my_block, but not the one I am looking for. This seems like there should be a very straightforward fix. Can anyone suggest one to me?

Thanks.