I did jelqing and other manual girth work for years and almost never got expansion after a workout. Maybe after a crazy hour long session I might get 1/8th of an inch, and that was rare. Despite that, I still gained 1/2 inch of girth.
It wasn't until the last year and a half or so, when I added pumping and clamping, that I started to see regular expansion after girth work. And not just after pumping and clamping, now I see it after manual work as well.
I'd suspect that for guys like me who aren't prone to fluid retention, nearly 100% of the post-workout expansion has to come from the tunica expanding. This is...not easy. It's tough tissue, and it takes a lot of force to make it expand. I think that after pummeling it with 2x a day clamping and pumping, my tunica has increased elasticity. At this point I can do a couple of dry jelqs and a hard clamp at the base for 20 seconds and get expansion that will last for a few hours.
Follow the link to learn more about: Girth program (SRT 5x5x3).