GEXF node sizes behaving strangely

[ptlambert]

I just started using Gephi, mainly to visualize graphs I'm emitting in the GEXF format. This works fine for the most part, but I don't quite understand the "size" attribute for node elements. The primer claims that this is a scale factor set to 1.0 by default (whatever that means), and a node of size 2.0 will appear twice as big as size 1.0. However, this is not what I'm seeing in the interactive preview visualization: The displayed node sizes are only roughly correlated with their size attributes. There's no rhyme or reason to it; the exact displayed proportions depend on the set of node sizes present in the graph (e.g., nodes with sizes 1.0, 2.0 and 3.0 will be displayed very differently and disproportionately from sizes 1.5, 2.5 and 3.5). I've wound up resorting to trial and error in order to get the displayed node sizes I want, and they're still not exactly what I seek.

Could anyone explain how the GEXF node-size attribute works and/or point me to some further documentation? Many thanks.