I think the secret to the audibly quieter sound of the Master Airscrew propellers lies in the different angle of the propellers from the original DJI. Mini 2 for 26 and 21mm replacements. This data can be read from the numbers on the propellers. This great footage from Tech Drone Media helped me understand this fact. Thanks Henrik.
The conclusion from watching this video is quite simple. I did not have to confirm this with my post. My point was to point out why the Airscrew propellers are quieter. These are just my conclusions.