Take a look at this thread:
https://forums.pelicanparts.com/porsche-911-technical-forum/778272-door-speaker-spacers-8.html
My setup: I have the spacer plate mounted to the door. The door card goes over that plate. I used a foam insert similar to above sandwiched between the speaker and the door card. The screws holding the speaker in place drive in to the spacer plate.