The largest pitcher on both my ventrata so far did a quick loop around the edge of the basket, very near but not touching the moss, then got huge. What I notice about it is that it had room to grow, without a lot of leaves or other pitchers in the way. It had one dying pitcher nearby for support for a while, but just long enough? Location, location, location? Just to throw something else out there. I don't know.
On the other plant, a group of large pitchers grew together hanging off the side of the other plant. I've posted pix of that clump. None are as big as that one though.
My personal feeling is that the overall health of the plant will determine pitcher size, which will vary naturally from pitcher to pitcher all the time. The pitchers on all my neps are growing bigger than when I got them.
I can't rule out the environmental factors on pitchers though. I've seen lots of potential pitchers get crowded by nearby leaves or pitchers, blocked by another plant, or get big seemingly out of nowhere. One ventrata leaf was looped by a confederate jasmine vine along a support chain about a week ago, which is holding the vertical growth of the whole ventrata up nicely. I'll be interested in seeing how that pitcher turns out.
Mostly the pitchers that grow right on the moss in my baskets are not the biggest. But, of course, there are a couple REALLY big ones, just behind that one I mentioned at the top. Just to add to the confusion...