That's interesting as I don't know of anyone (yet) who's using different tyre widths F & R
Could work well for lighter steering, but still have a good tyre contact patch for rear power delivery & grip
I have narrower tyres for the front due to the Crosshead issue... I run 1 Deg Neg Camber which adds to this issue.
The rears being larger help keep in control the added power of my Blue and White racer which is 285bhp... a flat upshift 2nd-3rd in the dry will result in wheelspin which I was keen to try to contain. I keep the same sizes between the two cars to try to control the quantity of tyres I have knocking around... at one point I had 5 full sets of wheels and wets/dry's for both cars along with around 6 spares.