Actually, the article in question is on the Anova site, but not the community forums (so, you could have just asked the question there in the comments section - as others did).
When discussing an article that isn't part of the community, you really should post a link to that article when you pose the question so people can reference exactly what you're talking about (e.g.):
And (now that I've reviewed that article), two things:
1) Answer to your question - putting it into the middle might provide slightly better water circulation, but it's very likely to interfere with any sous vide racks you may be using. Me, I like mine in the corner of the vessel - maximizing the amount of space available for the items I want to cook.
2) ChefNicole suggests a 2 3/8" hole saw - then use sandpaper to make the hole a little bigger if necessary. Me, I've been telling people to get a 2 1/2" hole saw. It's easier to find and (IMHO) does a better job. The PC can actually go all the way down to the vent ring - which won't pass the 2 1/2" hole, providing ample support. (and, if you want a nice snug fit for the pc, you can put some electrical tape on the cut edge, providing a very good seal).