Maybe…maybe not…
I have done 20min, I have done ramp. I have done 3 ramps in a single day across different kit in different environments. I have done all out 1hr/40km TT. I have done all out 20km TT.
The only surprising finding was that the results were NOT wildly different to whatever the comparative FTP was. A few watts here, a few watts there, or maybe even the same.
I really over thought this, so you didn’t have to 