ZHVelo

For most things, NP is a better indicator of overall effort than avg power. NP weights intense efforts more, to approximate how they're more taxing on the body. Generally does a pretty good job.

But for an FTP test, you use avg power, what you actually did.

The 95% of a 20 minute effort works well for some people and not for others, depending on your stamina, aka ability to resist fatigue.

Someone else can probably give you a better idea what you can expect for improvement with training.