You might be interested in reading this paper: https://people.freebsd.org/~seanc/postgresql/scale15x-2017-p...

I am interested and I appreciate the thought and link, however these appear to be the slides to a talk without the actual talk. If so they are of limited use because the slides never have all the information the presenter has, and that information is often just a summary.

Is this the correct talk: https://youtu.be/dwMQXLOXUco?t=5380 ?

Yes, sorry about that, that is the corresponding talk to the slides. Thanks for pointing that out.

First, you have to make sure the page sizes for the FS and DB match. That's a critical requirement. But yes, you'll get write expansion twice.