I might have found it myself. WP lists this very promising page about Publicize and it says to open Google+ (in a browser, not smartphone!) and then go to Settings > Manage apps & activities.

I'm on mobile now so I'll check this from home and confirm.

I might have found it myself. WP lists this very promising page about Publicize and it says to open Google+ (in a browser, not smartphone!) and then go to Settings > Manage apps & activities.

I'm on mobile now so I'll check this from home and confirm.
update: Yes, this is how to change the audience for new WP posts. The circle choices are:

• Public
• extended circles
• your circles
• your organization (if you're a Google Apps user)
• only you
• custom (this is where you can specify any mix of circles you like)