FTB will be shutting down this forum by the end of July. To participate in our community discussions, please join our Discord! https://ftb.team/discord
You posted the page for the Aura Aspect, not Aura nodes.
http://thaumcraft-3.wikia.com/wiki/The_Aura
This is what you want, and even then the page you wanted to link clearly states:
Small nodes merging can actually lose aura. The issue here is that you would expect the new node to be...