Isn't the rolling radius of the 18s and 19s broadly similar due to the 19s having lower profile tyres? If so, then the effective fill of the arches is the same, just that you see more allow with the 19s which does give the impression of a fuller arch. Regardless, I've only got 17s on my current Mk5 GTI, and if my mates Ford Focus is anything to go by, the 18s on his still leave a huge gap around the arches, and they don't even curve around the wheels properly! All-in-all, very happy indeed with the overall look of the 18s.