Two chicks 11 weeks old, an 8' x 16' run and some mature hens, some of which chase the young ones. The chasing is the part that would worry me too. Many hens will peck or run off a chick that invades her personal space so chicks usually quickly learn to avoid the hens. A big part of your problem could easily be that they don't have enough room to avoid the hens or run away from them if they get chased. Integration can be a lot harder when room is tight.
I'd also have tried to just let them out after they have been in a see-but-don't-touch situation like yours. That usually works for me. Where are they being attacked? Inside that hardware cloth enclosed area or out in the main run? It sounds like the hens don't wait until their personal space is invaded, they attack as soon as they get a chance.
Can you identify a ringleader? One specific hen that is attacking or attacking first. If you can, isolate her and see what happens when she is not in the mix. That may at least tell you where your problem is. Sometimes isolating a troublemaker for a few days knocks her down in the pecking order so she is no longer a problem. It doesn't always work but it is worth a try.
Is this the one they go after? Sometimes mature hens will attack a male chick once he gets old enough for them to see that he is male. Some people call that "schooling" him to teach him respect for the hens but it can result in seriously injured or dead chickens. He is a little young for that but some cockerels mature early. With your fairly tight space he does not have enough room to get away and stay away. If this is the case my only suggestions are to either get rid of him or keep him locked up until he matures enough to take over the flock, probably around 7 to 8 months of age.
Sometimes the one attacking is the dominant hen, making sure she stays dominant, especially if she is going after a male. Sometimes it is one at the bottom of the pecking order, she does not want one of them to rise higher than her lowly spot. I don't know what is going on so I don't know the best way to approach it. Isolating an aggressor is often a good start.