When setting the maximum number of profile posts to display on the forum list, you can set any number, or zero to disable its display. If you set that option to 1, only one profile post will show. But the query still limits the results to 10. The limit only changes when you increase the option to 6 or greater. Why do the results get fetched and then sliced later on? Also, there is no upper maximum value for this option - either in the option parameters, or elsewhere (not that there would need to be).