Quire 13

[Searcher]

I noticed something while reviewing Q13 that I hadn't seen before. It seems so trivial that you don't even notice it: Not all nymphs are standing in a tube or basin, a few are standing on it.  It doesn't matter if they have liquid under their feet or not ( You are not allowed to view links. Register or Login to view. (2x), You are not allowed to view links. Register or Login to view. (4x), You are not allowed to view links. Register or Login to view. (1x) ).

I believe that it is important how the nymphs stand although I have no idea what it is all about.

Actually I wouldn't surprised if it is so. The same as the nymphs in the Zodiac circles: 80 human figures are in tubs, two – on tubs and two more – behind tubes/tubs. 
Nymphs in tubs: 10 - in the horisontal ones, 70 - in the vertical ones.
One female figure (in Gemini) is depicted standing in a pool, the next two figures (dressed male) are depicted standing on the horizontal tubes/tubs.
One of the nymphs (in Virgo) is depicted standing in a tub.
There are two rough tubes behind two human figures (Sagittarius).
Supposing Quire 13 to display some actions with liquids, we can also assume that the nymphs show their state and behavior. 
Calm nymphs (quietly sitting, directed in one direction) can mean a calm, stable state in the liquid, nymphs directed in different directions, randomly waving their hands, fighting nymphs can reflect some kind of violent struggle process inside the liquid. So, the position of the nymph relative to a tub can also have any meaning, but I'm not yet ready to guess which one.