Sheep are thick as hell and although not a heli pilot I would say that you can't be sure what they will do ever.
In general they should flock together. Where that will actually go is in the hands of god.
Lambing time they are more thick than usual so if you get between a mother and a lamb she will go to the lamb away from the flock.
They are also very susceptible to known factors so if the field is used regularly they won't react at all. If its a one off they will react.
If you go to any artillery range they all have sheep grazing on the target areas. They don't move with 105mm HE coming in. Put a smoke down and all hell lets loose.