He is right
But the problem also goes away if you fit the same size tyre front and back, then you can fit whatever tyre you want without any traction issues. IMHO the alloy engine cars do not need the staggered tyres, especially the saloon. I am on a square setup of PS4S and it is more than fine. RS3 did come as standard with square 235. Staggered was an option code (at least on my 2018 it was)
If you want staggered tyres then yes you need the RO2, no traction issues but no inside tyre tread either unless you drive really carefully. There is an RO2 Continental but not sure it is any better.
Hope you enjoy Goodwood, cracking place to be