Using percentage of FTP (which is usually based on another percentage) to deterimante zones is practical and fine for a lot of people but for some is not even close… I did a lot of lactate testing and ride analises and found that is not strange to find upper zone two to be for example 260w and FTP to be 290w…
On the other hand I currently have an athlete who cannot hold 170w without big HR drift but doing 4m intervals at 420w…