I just thought I'd share my experience the other day adjusting the nib of a pen that was writing a bit dry.
I was finding that at first, the nib would write well with plenty of shading. But after having written a little without stopping, it would become dryer to a point where the ink was a little pale and there was almost no shading. I tried following the pen manufacturer's (TWSBI) example video on making the nib a bit wetter, but it didn't work.
I'm new to this, but I decided to inspect the nib myself using a loupe and do what I thought might help the situation. I found that there was a gap between the nib and the feed, and that I could see through the breather hole to the other side of the nib (even though the pen was fully assembled). Basically, the nib was lifted up from the feed. I'm not sure whether this matters much for capillary action, as long as there is *some* contact between nib and feed, but I decided to bend the nib a little to match the profile of the feed.
After having done this, there is better (albeit not perfect) contact between the nib and the feed. In addition, the slit in the nib was misaligned with the slit in the feed, so I fixed this as well. I find now that the pen writes with noticeably more wetness and consistency, although it is not perfect.