I have never seen a "flock" of migrating Monarchs. I watch wild areas that have LOTS of flowers (yellow sunflowers - the smaller ones) and observe MANY, MANY Monarchs floating from flower to flower.
Yesterday, it was a cool, dewy morning and I thought I would just try!
What I observed was about 30 Monarchs over this area (I think the sunflower is a "tall showy SF) I got my pants and shoes and sox SOAKED! BUT I did catch, tag and release only TWO of them. The area was too thick to try to walk into very far! Besides, the spiders yell at you!
So I got out of there. Some of the Monarchs were very low at the edge of this area - probably because of the breeze.
I think NJ is about on the same lat as Ohio, so just keep trying.