Take a look at this picture, which shows Vykkers and Glukkons to be about the same height - at least Vykkers to be the same height as Molluck, who in all fairness could just be a tall Glukkon. I also noticed that because of the way Vykkers' necks join their bodies, they can actually make themselves taller or shorter like a crane-type thing.
In the Auction Hall, that could just have been a small Vykker, or a tall Glukkon.
Just some more observations.
EDIT: Forgot to attach the picture.
