Try hanging 2 or 3 feeders in a loose group--a few feet apart. With that many birds coming, the birds will find it impossible to defend the feeders. I think they realize that they're spending all their time chasing and not getting any eating time, so they give it up and get more sociable.
Are you far enough south to have hummers all year, or do they all split for winter? We get hundreds in summer but this time of year we're at about the end of our season.
It's sad to see them go, but I always worry about the stragglers. We had a hard freeze the night before last and we still have one cute but naive adolescent hanging around...