I cannot talk for coach Matt or Coach David, neither am I a coach. I can only share my (limited) experience 😀
My understanding of the 80/20 system is, that the intensity and zones are based on the described threshold tests that can be found here. I was initially using a slightly different FTP test (Coggan 20min test) but ended up switching to the 80/20 test as otherwise the Zones would be slightly off due to the test giving me (in my case) lower FTP. Here you can look at the discussion I’ve had with David.
Long story short: Use the 80/20 protocol.
Sorry if this isn’t what you wanted to hear. Happy reading.