You’re right that the documentation isn’t necessarily the best. Another useful plugin for better Fediverse dovetailing is to use the NodeInfo plugin by Matthias as well. It helps by providing some additional details about your instance to the broader Fediverse. For example, you’ll see your site show up on the-federation.info where you’ll also see a number of other WordPress sites/users who are in the Fediverse as well. I’d heard rumors that portions of this were moving into the main ActivityPub plugin, but haven’t seen confirmation of all of it.
For those going the cross posting route and using Mastodon Autopost and Mastodon Auto Share I’ve written up some details for Crediting your own website when syndicating to Mastodon with WordPress plugins.