I'm not sure what the overall policy is (or if there even is one). If you're at $400, and a couple is at $500, and they need two and the couple won't split up, they'll take them. If I'm also volunteering, at, say, $800, most GAs would take the couple ($1,000) rather than us ($1,600), but at your home airport I don't know how strong their preference for you would be.