The ramp test is skewed towards short (e.g. 1-5 minute) power. So it’ll likely give you an overestimated figure if you’re good at that, and an underestimated one if you’re not.
The only good thing about the ramp test IMHO is that there’s no pacing involved, unlike the 20 minute test which is very hard to judagey, so usually needs a few goes to get so you can empty the tank by the very end and not before.