To modify the threshold parameters, go the YARRP settings page and then click “screen options” in the upper right-hand corner of the page. Check the box to show “relatedness options” and this will display the options tab for whether YARRP should consider tags, categories, etc.
talkstory, you’re an angel. I would never have thought to look at the Screen Options. It’s a bit unintuitive that it’s set up that way. Maybe there should be a notification on the Settings page telling users there are more options hiding somewhere.