Couple of observations on under-performance in the TR ramp test.
Firstly, while it may be conservative for threshold, I find that it sets my numbers for vo2 workouts perfectly. And vo2 workouts form an important part of Sustained Power Build.
Secondly, there’s a ramp test you can get on Zwift and can probably build in Workout Creator. It has longer steps, and the failure point comes at around 121% of FTP rather than 133% for the TR ramp test. I’ve found it gives me a higher number that probably better represents my actual hour power - but as above, beware putting that number in before doing Shortoff +4 or something.