Ramp test calculations = 75% plus?

Just curious as to whether anyone knows what the actual calculation is for the Zwift Ramp Test? I understand it to be approximately 75% of the last completed 1 minute effort. However, I assume it also takes into account a portion of the last effort that you failed at? Otherwise there would be a lot of people with the exact same estimated FTP, if they all failed on the same ramp. i.e. I completed the 340w step and then very early into the 360w test I exploded. Based on 75% of the last 1 minute (340w), my FTP should be 255w. However, Zwift advised that it was 257w (roughly 75% of 343w).
If I test again and again only reach 340w BUT go for a slightly longer period in the 360w stage, will it calculate it as being higher? The reason being is that at 75% of 360w my FTP then goes to 270w. I suspect I’m more likely to be between 257 and 270 though and would want to see some increase, even though I “failed” at the same point.

Assuming it’s using 75%, it would be 75% of your 1min power. Are the ramp steps 1min long? For discussion, let us assume 1min ramp steps. The test does not look at the last completed 1min step. It looks at 1min power. So if you partially completed a step, that would be taken into account.

If you look at the post ride Critical Power curve, take the value from 1min and multiply by .75. Sometimes, that graph is incorrect (bug ??). So if you also upload to Strava, Garmin Connect, etc., you might want to look at the 1min power there.

Lastly, the test is an approximation of your FTP. If after a few workouts, you find the workouts are too difficult or too easy at that value, then manually adjust it up/down.

Thanks for the response. Yup I’m basing this on the Zwift ramp test, which is 1 min steps that increase by 20w each minute.
I accept it’s an approximation and there are a multitude of things that can vary that test at any one time. I guess I just wanted to understand how they were coming up with the FTP figure that they list on screen after your test.
Cheers