form score

can someone (hopefully from EA) tell me how the form score is calculated? I have a defenseman and at the start of the regular season I'm supposed to maintain a form score of 75. I've played 3 games. the first game all the coaches ratings were in the green and I believe I had a total grade of 80 something but only got a form score of 50 for chapter average and 50 for chapter target. second game I got somewhere in the high 80s again for the overall grade but scored a goal. the CA (chapter average) went up to 75 and the CT (chapter target) went up to 75. third game I got an overall grade of 83 but did not score but now my CA went down 5 to 70. there is a 3rd column the has "DELTA" and it shows 5 point down. why did it go down if I'm getting higher than 75 in the coaches overall grade for a game? all my scores were in the green as well.