I think a top down track of the two aircraft would show the helo altering course INTO the plane. Just sayin'. A side view does not give a very good perspective of the aircraft tracks. If we have flight data combined with GPS, it should present a pretty clear indicator of how it went down. I bet it would show the helo altering it's flight path to intercept the plane. I would think that an increase in helo airspeed in order to intercept the plane is probably likely as well. You have to lead a moving target.
You would think that at the very least the chopper would change altitude.