Bait ship. Get all the ships chasing bait (a damaged ship out of 6) and the other 5 can kill everything else. As long as you are not in their firing arc they won't shoot you. And if your other 5 ships do not take damage they will not attract attention from any other ship except to get shot at if they enter a firing arc.
I tested a few things out for you. Harriers get chased instead of Corvettes. Damaged ships get chased instead of full health ships. Use that to your advantage and killing the Rancors is a piece of cake. In fact, I found the Gens to be infinitely harder to deal with because of their massive firing arc. But I did something interesting and went circling within their firing arc fast enough the Rails could not hit me, while my lasers tore them apart.