Our T5.1 came with 235/55 so that is what I always put on it. Now I have bought a brand new set of of VW Thunders to put on it so I can take my painted set off when I sell it. The new ones came with brand new unused 225/60 as OE.
It really seems like they put on whatever they get a good deal on that week.
I am going to stick with 235/55 - seems to me they give the correct circumference for the maximum tread witdth.
I did wonder if the reduced tread width is a sop to rolling resistance and BlueMotion but I would rather go for contact patch. After all they say that BM includes low rolling resistance tyres but I don't see any evidence of that, indeed some OE fits are pretty poor on fuel and noise rating so hardly BM.