I think it was just an example, and people usually do not spend their games filling shields with t2 pd's.
But if example on FAF's "chessboard" is not good, then:
Aeon t2 shield 20203.14=1256 superficy
Sera t2 shield 28283.14=2462 superficy
Sera one covers 1.96 times more surface. Considering space lost underneath the shield also, two Aeon shields covers less useful space than one Sera shield. And two Aeon shields cost total of 960 mass, and consume/drain 300 energy. While Sera one costs 700 and consumes/drains 250 energy. And of course you dont always have space to put small shields everywhere. Much easyer to have overlapping and "blinking " shields with bigger shields. And not so many units that can totally (and always) miss an Aeon shield bubble. I suppose t3 arty can miss it, but can also fall two times in the same place...
So, I would like to point out, that shield size can be huge advantage, on static as well as on mobile shields.
edit: calculation marks have dissapeared.? I mean 20 multiply 20 mutiply 3.14 and 28 multiply 28 multiply 3.14