I saw a good explanation of this one and I can no longer find it. My basic understanding of the post (which I agree with) was that you want it engorged, not erect. If there is any “hardness” to it, then you need to bring it down a level.
Now that being said, I almost always start my jelq sessions with a small flaccid and build up. As you start with the flaccid jelqs, more blood will engorge your penis until you have the biggest, fullest flaccid you can have without being hard at all. That’s where you want it to be and stay at for your session.
Jelqing with less is absolutely fine too. Less engorged flaccids still get benefit from the workout too.