So glad you found them helpful. So every instructor teaches this a little differently. Definitely do not retract as this makes your shoulders unstable. I personally like shoulders flat to the floor which means you don’t let yourself sink into the shoulder and a little protraction is necessary to achieve this but not so much protraction that it causes you to overly round the upper back. I created a great follow up video to this which you can find in the beginner program. The video is called “upper body mat flow: shoulder stability”