A great video. One thing that I have found when I was trying to get some better awareness and effectiveness of retracting and depressing the scapulae was to put arms up and out at shoulder level with the elbows bent at 90 degrees.
Then:
First, retract the scapulae and watch the hands and elbows draw backward.
Second, depress the scapulae and watch the hands and elbows drop slightly.
These visual cues backing up the attempt helped me a great deal in getting better control and awareness of what I was trying to do.